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MLR: Engines eBook

1. Page 60 of 67 MLR Engines eBook 2013 Melior Inc Unit 6 AIR FUEL DELIVERY SYSTEMS EXHAUST SYSTEMS AND EMISSION CONTROLS Chapter 1 Systems and Controls Air fuel Delivery Systems Air is provided to engine cylinders through various methods of induction Induction systems are matched or tuned to a particular application The air filter surface area throttle body bore diameter and even the tubing from the air cleaner assembly to the throttle body control the air charge volume to the engine Intake Manifold The intake manifold plays an important but different role in the air intake systems for Throttle Body Injection TBI and Multiport Fuel Injection systems All new automobiles sold in the U S since 1990 use fuel injection systems On engines equipped with TBI the intake manifold must carry both air and atomized fuel to the cylinder head intake ports Therefore intake manifolds for TBI systems like those for carbureted systems are designed with compromises to meet both objectives Wet manifolds as they are known must maintain proper velocity throughout the desired engine operating range to hold fuel in suspension while providing sufficient air capacity to obtain peak horsepower In the TBI system shown here the cylinder on the right is on its intake stroke You can see the air fuel mixture in both sides of the manifold and air fuel entering the right cylinder around the open intake valve The in
2. 000 000s01 mEtmnm mz mn nner ene slueeressseeceseeeenseseeeee 52 Unit 6 Air Fuel Delivery Systems Exhaust Systems And Emission COntrols sssccccssseceeeeeeeeeeees 61 Chapter 1 Systems and Controls c 0 c scsesssrersarerseres 0s tm hz _ _ lt i reese 61 2013 Melior Inc MLR Engines eBook 2013 Melior Inc Unit 1 ENGINES OVERVIEW Chapter 1 Engine Parts The engine is the power plant of a vehicle Automotive engines have gone through tremendous changes since the automobile was first introduced in the 1880s but all combustion engines still have three requirements that must be met to do their job of providing power air fuel and ignition The mixture of air and fuel must be compressed inside the engine in order to make it highly combustible and get the most out of the energy contained in the fuel mixture Since the mixture is ignited within the engine automobile power plants are called internal combustion engines Most can be further classified as reciprocating piston engines since pistons move up and down within cylinders to provide power This up and down motion is converted into turning motion by the crankshaft Basic Engine Parts A small engine such as one found in a lawn Camia EA Rocker Arm Cover Rocker Arm mower usually contains only one cylinder and nome n g Valve Spring Cam Lobes Exhaust Valve Engine Coolant Engine Block piston Automotive engi
3. A system can be in a Not Ready state because of previous repairs or a dead or recently replaced battery A vehicle will remain Not Ready until all monitored driving conditions are met Different manufactures have different procedures for setting readiness monitors Most will require a drive cycle Starting in 1996 through 2000 a vehicle can have no more than 3 readiness monitors not run and still pass an emissions test For 2001 to 2008 no more than two readiness monitors can be left in a Not Ready status On newer vehicles all monitors must be operated Most vehicles will display a P1000 DTC when tested if readiness monitors have not run Continuous monitors are always operating any time their enabling condition is met An example would be a misfire monitor A misfire monitor would illuminate or flash an MIL if a misfire is severe enough to damage the catalytic converter However there is no need to operate a misfire monitor when the engine is not running These are some of the major monitors run by the PCM in an OBDIl equipped vehicle Depending on the manufacturer and vehicle there may be more major monitors Always refer to the vehicle service manual for a list of monitors and their enabling condition e Catalyst Efficiency e Comprehensive Component Monitor CCM e EGR System e Evaporative System EVAP e Fuel System adaptive fuel system trim e Heated Catalyst e Heated Oxygen Sensor e Misfire Detection e Secondary A
4. can be compared from cylinder to cylinder to detect abnormal or uneven wear Cam bearings and journals can be measured and inspected with the cam removed Notes e Manufacturer s specific service procedures detailing component and fastener removal sequence component inspection and fastener torque should be followed to the letter e Be sure to mark rocker arms and or cam followers and keep them in order during disassembly and inspection Do not mix them up when reassembling them Match them to the same cam lobe that they were removed from Failure to do this will cause rapid cam lobe rocker arm and or cam follower wear e The contact surfaces of the cam lobes and rocker arms and or cam followers are some of the highest friction points in an engine If a cam lobe is worn replace the cam and ALL rocker arms and or cam followers Never run used rocker arms and or cam followers ona new camshaft or new rocker arms and or cam followers on a used cam Rapid wear will result Page 26 of 67 MLR Engines eBook 2013 Melior Inc Inspecting Pushrod Valvetrain Components A visual inspection of the camshaft itself in a pushrod engine requires that the camshaft be removed If a worn cam lobe is suspected pushrod travel for each valve individually can be measured with a dial indicator while rotating the crankshaft A visual comparison of how far each pushrod and rocker arm moves as the crankshaft is rotated may be enough to find
5. is OFF A series of 8 bits makes up a byte also called a word The wire s that carry the serial data messages are called the data bus Besides allowing control modules to communicate with each other the data bus also allows the technician to tap into the data stream to run system diagnostics by connecting an electronic scan tool to the Data Link Connector DLC DLC CONNECTOR The DLC Connection The DLC Connector OBDII Since Onboard Diagnostics II OBDII was mandated in 1996 to reduce emissions 1997 for overseas imports all vehicles sold in the U S have a standardized DLC connection located somewhere on the driver s side below the instrument panel OBD II compliant vehicles use the same standard for connections trouble codes and terminology OBD II guidelines require a vehicle system to have the ability to record a snapshot of operating conditions when a fault occurs and the system must permit codes to be cleared with a scan tool The speed at which bits are transmitted in the serial data stream is called the baud rate a measure of how many bits are transmitted per second Early Engine Control Modules had a baud rate of 160 Starting with the 1986 model year ECMs with a baud rate of 8 192 were introduced which is clearly a much higher serial data transmission speed A common data stream for OBD II vehicles has a baud rate of 10 4K or 10 400 bits per second also known as Class 2 data stream The next serial networks t
6. 67 MLR Engines eBook 2013 Melior Inc Common causes of spark knock include low octane fuel carbon deposits in the combustion chamber high compression ratios and high cylinder temperatures Spark knock causes a rapid rise in pressure and temperature that can damage spark plug electrodes pistons rings valves and valve seats While spark knock is not as damaging as pre ignition the high combustion temperatures of prolonged knocking may lead to pre ignition in severe cases Spark Timing Spark timing must change to account for different operating conditions such as engine speed and load The time required for combustion remains fairly constant so this means that as engine speed is increased the spark which would normally occur just before the power stroke begins must happen earlier in the compression stroke Ignition timing is referenced in degrees and earlier timing is said to be advanced while later timing is said to be retarded On many DI systems the initial timing or base timing is adjustable and must be set to a specification The vehicle s computer or powertrain control module PCM or other mechanisms automatically handle the necessary changes in timing to match the operating conditions The base timing specification is usually several degrees before TDC Engines with El systems have no base timing adjustment Incorrect spark timing can cause abnormal combustion and excessive timing advance can cause spark k
7. Scan Tool These will be discussed in the following section Page 56 of 67 MLR Engines eBook 2013 Melior Inc e Vacuum Pressure Gauge for measuring and testing engine manifold vacuum and other components We will discuss this further in a later section e Compression Tester for measuring cylinder compression We will discuss this further in a later section e Cylinder Leakage Tester for pinpointing sources of leakage in combustion chambers e Dynamometer A large machine the vehicle is operated on that can load the engine to measure road performance characteristics e Oscilloscope A scope provides a visual display of voltage over time on a monitor The pattern displayed can be analyzed in various ways Once used mainly for diagnosis of secondary ignition systems it can be very useful in analyzing many other signals such as sensor outputs e Exhaust Gas Analyzer Most measure the percentages of five different gasses in the exhaust stream HC CO NOX O2 and CO2 The makeup of the exhaust gas can be a useful tool in diagnosing the causes of excessive emissions as well as drivability issues e Engine Analyzer Combines several of the above tools into one console Scan Tools A scan tool is a handheld device designed to help diagnose computer controlled systems on vehicles OBDII vehicles supply power to the tool through the pin connection some older vehicles provide power through the cigarette lighter S
8. already occurred Therefore high mileage engines are best replaced or completely reconditioned the first time Page 39 of 67 MLR Engines eBook 2013 Melior Inc Chapter 2 Cooling and Coolant Leaks A vehicle chassis is made up of several systems that all work in unison to provide a safe and comfortable ride The chassis includes the frame or unibody brake system steering and suspension systems and wheel assemblies Engine Related HVAC Engine Cooling and the Heater System There is an abundant supply of waste heat produced in the engine This waste heat is expelled into the exhaust system and absorbed into the engine parts and oil The heat that is absorbed by the engine parts must be removed or the engine would fail in minutes This is the job of the engine cooling system We can tap into this heat source to provide heat to the passenger compartment On vehicles with an automatic transmission the cooling system is also usually used to cool the transmission fluid We will not be providing a full discourse on cooling system service here but since the HVAC system is really all about heat a brief discussion of the cooling system is a good place to start The Cooling System An engine burns cleanest and with the least wear when at its normal operating temperature of around 200 degrees F 93 C The cooling system is designed to allow fast warm up and then maintain this optimum temperature This is accomplished with a thermo
9. are included here Intake Manifold Gaskets Oil can enter the intake manifold at any point where oil is close to a leaking intake manifold gasket Most but not all V type pushrod engines are designed so that the intake manifold covers the valley containing the camshaft lifters and pushrods Intake manifold gasket failure on these engines can allow manifold vacuum to suck oil past the leaky gasket into the intake ports where it is delivered with the air fuel mixture to the cylinder Some versions of the GM 60 degree V6 and Ford V6 and V8 engines are designed so that the intake manifold to cylinder head gasket is underneath the valve cover This creates two potential paths for oil to enter the intake runners A failed intake gasket can cause oil to be drawn from the valvetrain area under the valve cover and from the area underneath the intake manifold itself Oe Ee wns pel We x Yee SL Page 34 of 67 MLR Engines eBook 2013 Melior Inc Propane Enrichment Pinpointing intake manifold gasket leaks can be difficult A propane enrichment tool and exhaust gas analyzer can be used to locate them To find the leak remove the PCV valve from the valve cover Leave the vacuum hose connected to it and temporarily turn or orient the valve so that it draws in clean air rather than crankcase fumes Next connect the Exhaust Gas Analyzer as per the analyzer manufacturer s instructions Start the engine and a
10. called a centrifugal advance to advance the timing for faster RPM and a vacuum advance mechanism to advance the timing under lighter loads These adjustments are made by the PCM on today s cars Below is an animation of a DI system with electronic triggering and switching 1 Spark plug wire 2 Distributor cap 3 Rotor 4 Coil wire 5 Distributor beneath cap be 4 La w 6 Distributor shaft and timing disk trigger wheel 7 Pickup coil 8 Control module 9 ignition coil 10 Spark plugs MJ SL be O 10 O 10 O10 H10 0l J Fl eF EF EF FF SHAFT PICKUP COIL SHIELD BOTTOM VIEW OF DISTRIBUTOR CaP INSPECT THE CAP AND Page 48 of 67 ROTOR FOR CARBON TRACKING MLR Engines eBook 2013 Melior Inc El Systems El systems go a step farther eliminating the need for a distributor cap rotor and sometimes spark plug wires Like some later DI systems these systems use input from a crankshaft sensor CKP and often a camshaft sensor CMP and other engine sensors for trigger timing Ignition is controlled by an electronic control module IC and or the PCM IGNITION CO In El systems multiple coils are used Some systems use one coil per DANA EIE a spark plug while others use one coil per pair of spark plugs Systems that use one coil for two spark plugs have pairs connected in series and both spark plugs fire at the same time One cylinder wil
11. gear drive arrangement should be replaced as a set as well Mixing new gears with old worn ones will result in increased noise and accelerated wear Engines that use a toothed belt sometimes there are more than one to drive the camshaft generally have a recommended belt replacement interval Consult manufacturer s service information for this information Timing belts also sometimes drive other engine components besides the camshaft s This varies with engine design some designs use the timing belt s to drive the water pump oil pump or balance Shafts Belt breakage can occur if any one of these components seizes Timing belts can also become oil or coolant soaked if nearby gaskets or seals are leaking Failure to fix the leak before replacing the belt will result in rapid deterioration and possible premature failure of the new belt Any time a timing belt is being removed it is good practice to replace it regardless of age An exception to this would be if the belt has recently been replaced and is being removed to access another component When and if in doubt replace Any vehicle that comes into the shop with a broken camshaft drive belt or chain should be checked for valvetrain or piston damage Vehicles where the belt or chain didn t break but got loose enough to get the crank and cam severely out of time should be checked as well Some engines use what is called an interference design This means that if the crank and cam ge
12. task The computers in vehicles are no different They receive input data from various devices such as switches and sensors that provide information regarding conditions such as e Engine load e Gear range e Engine temperature e Speed The computer also performs specific output functions such as e Metering fuel e Adjusting timing etc e EGR operation e Control transmission shifting Computers use voltage signals from the inputs and send signals to output devices Two types of signals are involved analog and digital Incoming analog signals must be converted to digital format for the computer to use the data Output digital signals may be modulated by frequency or pulse width One of the bigger chips is the Microprocessor Unit MPU which may also be called the Central Processing Unit CPU Service on some of the newer models may involve reprogramming or changing the calibration in the PCM It is necessary to refer to the vehicle service information for these procedures Various computers in an electronic system communicate by means of a serial data stream Serial data is a string of information transmitted in sequence one item at a time making up the data stream In electrical terms serial data consists of voltage signals changing between high and low or ON and OFF Page 52 of 67 MLR Engines eBook 2013 Melior Inc Each individual signal either a 1 or a 0 is known as a bit A 1 is ON and a 0
13. the calibrated spring loaded valve off its seat releasing coolant into the overflow reservoir tank When the radiator cools down the reduced volume of coolant creates a vacuum in the radiator pulling open another valve that allows coolant from the reservoir tank to flow back into the radiator 3 PRESSURE PRESSURE RELIEF FAILURE CAUTION If an engine runs very far outside its optimum temperature range either too hot or too cold for very long drivability and emissions problems can occur in addition to severe engine or other system damage If a vehicle s temperature warning light should illuminate or the gauge rises into the red or hot zone turn the engine off at once Note also that it is possible for an engine to overheat without illuminating the warning light Excessive engine pinging very hard or swollen hoses boiling in the overflow reservoir or escaping coolant or steaming from the system are indications of overheating CAUTION e Never attempt to remove the radiator cap with a warm engine with the engine at operating temperature or higher Severe burns can result Ensure there is no pressure on the system before opening the radiator cap See your instructor for tips on determining system pressure and temperature e Antifreeze is poisonous and especially toxic to animals Page 41 of 67 MLR Engines eBook 2013 Melior Inc Inspecting and Testing the Engine Cooling System Inspecting and testing th
14. GASES ami COMBUSTIBLE MIXTURE TO INTAKE MANIFOLD TO CRANKCASE Exhaust Gas Recirculation EGR systems have been used on vehicles for many years The primary purpose of the EGR system is to control combustion chamber temperatures thus reducing the amount of oxides of nitrogen NO x in the exhaust Although EGR is necessary to control NO x emissions it also affects volumetric efficiency Volumetric efficiency is the ratio of the amount of air fuel mixture that actually enters a cylinder to the amount that could enter under ideal conditions An EGR valve provides a link between the air intake and exhaust systems Air flowing into the engine through the throttle body enters the intake manifold When the EGR valve is opened some exhaust gas is directed into the intake as well As the piston moves down the cylinder on the intake stroke the combination of air fuel and exhaust gas enters the combustion chamber This combination has the same volume as a pure air fuel charge but there is less air and fuel to burn when the mixture is ignited due to the presence of the exhaust gas Temperature and pressure in the cylinder are reduced resulting in reduced NO x However pressure in the cylinder is what pushes the piston down therefore engine performance can be affected by the decrease in cylinder pressure Page 66 of 67 MLR Engines eBook 2013 Melior Inc An EGR valve is designed to operate under engine lo
15. MLR Engines eB Table of Contents Unit 1 Engines OvervieW ssssssssessessessessessessessesseeserseesersresresse Chapter 1 Engine Parts cccccssccccssseccccsscceceseceeseseceeeeneeeess Chapter 2 Engine Classifications ccscccccsssececeseceeeeeeeeees Chapter 3 Mechanical Diagnostics ccccccssseceeeeseceeeeeeeeees oe eee ssssvececesresaversansseieiee el Unit 2 Engine Components Inspection And Repair 08 cso pole eat 5 Chapter 1 Engine Components ccccccesseccceeseeeceeseceeeeeeeees sononecdsl eee 16 Chapter 2 Inspection and ee sce iiaeccccecsvescvaaveconrarene 20 Unit 3 Engine Lubrication Cooling And Related Leaks ccccccsssccccsssececesececeeesccesenscceseuecesseeceeeees 31 Chapter 1 Lubrication and Oil LeakS 01ss esscseree00s01 6 mmn z oznm zhane sereeeeseseeeeeseseneeseeee 31 Chapter 2 Cooling and Coolant Leaks 0s c s0ss s000s01 1 Emm mmm nnrtnee te sueseeevedeesesseeeeseseaeee 40 Unit 4 Combustion And Ignition Systems cc ccssresseeereer0 ftttntttmmmm MMe PODbesepeusaeersaseseecesssseresseseeees 43 Chapter 1 Characteristics of Combustion 0000 000s01 AO 43 Chapter 2 Ignition Systems cccscssscrcsersersssererersrsenes es e AODREN 46 Unit 5 Computer SySteMs ccsscosscsssccsscesccescrescrescsesceescees cee MA 51 Chapter 1 Computer Systems and OBDII
16. This has made diesel engines attractive to automobile manufacturers at times but these engines have other drawbacks that have prevented them from taking over in passenger cars High exhaust emissions of particulates soot and oxides of nitrogen NOX due to the high combustion temperatures are an obstacle Difficulty in starting diesel engines in cold weather sluggish acceleration smell and noise are other factors that have prevented diesels from being widely used in automobiles but this may change again in the future Rotary Engines The rotary engine is one of the few mass produced automobile engines that is not a reciprocating piston design Instead combustion directly causes the rotation of rotors within a chamber This design can Page 7 of 67 MLR Engines eBook 2013 Melior Inc produce a very powerful smooth running engine with fewer moving parts than a piston engine and it can operate at higher RPM Movement of the rotor produces a low pressure area at the intake drawing in the air fuel mixture Further rotor movement compresses the mixture and it is ignited The resulting power pulse pushes on the rotor The rotor continues turning to expel the exhaust gas Three power pulses are produced for every revolution of the rotor a Exhaust So Fuel Intake Number and Arrangement of Cylinders Automobile engines can have three four five six eight 10 or 12 cylinders More cylinders mean more power strokes per revo
17. a worn cam lobe Pushrod Rocker Arm x Pivot and Stud Lifter or Tappet Camshaft Rocker Arm Visually inspect all rocker arms for signs of scoring or excessive wear at their contact points The example engine shown here uses a separate pivot which should also be inspected for excessive wear Some rocker arms are shaft mounted the shafts need to be closely inspected as well Excessively worn parts should be replaced In some instances the bearing that contacts the rocker shaft can be replaced In other cases the pad that contacts the valve stem can be replaced The example engine shown here uses pressed in studs to mount each rocker arm and pivot The installed length of all pressed in studs should be measured to be sure that they have not started to back out of the head If any stud is significantly longer than the others the head must be repaired by a qualified machinist Attaching Hardware Some engines use screw in studs A popular performance modification to small block Chevrolet V8 cylinder heads is to convert press in studs to the screw in type Screw in studs are less likely to pull out when used with high lift camshafts and stiffer valve springs Other engines use bolts and pedestals to retain the rocker arms Regardless of the attachment method all attaching hardware and threads need to be inspected for wear and distortion This includes threads in the head If there s any doubt as to the condition of the
18. ad when NO x is most likely to be produced as the result of high combustion chamber temperatures If the EGR valve opens during idle or low RPM effects on engine performance may be noticeable One benefit of the EGR system is that cooler combustion temperatures help the exhaust valves stay cooler Some engines do not use an EGR valve In such applications low NO x levels are achieved through a combination of engine design and computer calibrations of fuel control and timing With the appropriate valve overlap cylinder temperatures are controlled and emissions reduced These are only some of the major subsystems of emission controls some vehicles may have other systems An exhaust gas analyzer can be used to measure the percentages of different gasses in the exhaust stream Most machines measure the three main pollutants along with the amount of oxygen O2 and carbon dioxide CO2 for reference The makeup of the exhaust gas can also be a useful tool in diagnosing the causes of excessive emissions as well as drivability issues CAUTION It is against federal law for an automotive technician to remove or defeat emission control systems It is also illegal to manipulate data or falsify records in order to issue a pass on a vehicle emissions inspection in states where they are required Page 67 of 67
19. alve springs valves sticking in guides Page 59 of 67 MLR Engines eBook 2013 Melior Inc Excessive vibrations at idle Worn valve guides speed but steadies at higher Excessive vibrations at all rom Leaky head gasket Needle oscillates slowly or Intake system leak drifts between 3 and 9 inches HG lower than normal Normal at idle speed but drops Restriction in exhaust system to near zero and rises to lower than normal Intermittents Conditions that are not always present are considered intermittent These may be resolved by observing history DTCs evaluating the symptoms and reviewing conditions described by the customer Simulating system conditions to duplicate the intermittent and using a systematic process is important Follow the suggestions for intermittent diagnosis in the service manual Most professional scan tools and DVOMs have excellent data capture capabilities that can help you detect intermittent conditions When no trouble can be found and the vehicle seems to operate normally it is most important to verify that the condition described by the owner is normal compared to other vehicles The condition may be intermittent so verify the complaint under the conditions described by the customer before the vehicle is released When the problem cannot be successfully located or isolated a re evaluation is necessary The problem should be verified again by repeating one or more of the initial steps
20. ation of movement on the dial Valve guides can also be measured for roundness and diameter using a small hole measuring gauge lf wear is detected a micrometer can be used to measure the valve stems for wear and taper Micrometer use is covered in the Today s Class Brakes course Replace all valves that have stems that are worn or tapered more than the vehicle manufacturer s published specifications If the valve stems are tapered and the guides are worn new valves can often be purchased with oversized stems The valve guides can then be reamed to the right diameter to fit the new stems Some valve guides are replaceable Integral or non replaceable guides can be reamed out and then bushed back down to factory size using an insert Cylinder Head Reinstallation As with cylinder head removal there are so many different vehicle designs engine and drivetrain configurations and other variables that it would be impossible to come up with a valid generic set of reinstallation instructions Key points and reminders are noted here e When reinstalling a cylinder head follow manufacturer s specific published service procedures and instructions for the vehicle that you re working on e Also follow standard safety guidelines and procedures when using engine cranes and stands lifting equipment and safety stands Page 25 of 67 MLR Engines eBook 2013 Melior Inc e Manufacturer s specific service procedures detailing compone
21. attaching hardware and pivots they should be replaced Pushrod Carefully inspect both ends of each push rod Make sure each end is smooth and rounded Any roughness or distortion is reason for replacement Roll each pushrod on a flat surface after removing them Push rods that are bent do not roll smoothly Replace all bent push rods When reusing push rods make sure that they are clean inside if they carry oil to the rocker arms as with a small block Chevrolet V8 for example Lifter or Tappet You will typically find two types of lifters in most modern engines Page 27 of 67 MLR Engines eBook 2013 Melior Inc Flat tappets are not truly flat They have a slightly convex base that contacts the camshaft lobe Flat tappet camshaft lobes are ground at an angle close to that of the convex tappet base This is done to rotate the lifter in its bore with each valve opening closing event which promotes even contact area wear Visually inspect the valve lifter base or roller for roughness and damage If any damage is found on any lifter that contacts the camshaft replace all of the lifters and the camshaft Notes e Manufacturer s specific service procedures detailing component and fastener removal sequence component inspection and fastener torque should be followed to the letter e Be sure to mark lifters tappets and keep them in order during disassembly and inspection Do not mix them up when reassembling them Match them to t
22. bearing clearances are excessive the protective film of engine oil that normally prevents actual metal to metal contact at the bearing surfaces can no longer be maintained The engine will begin to knock Diagnosing Excessive Oil Consumption Most vehicle manufacturers define excessive oil consumption as consuming or using a US quart or more of engine oil in 1 000 miles or less of vehicle operation Lesser rates of oil consumption are considered normal operation in almost every case Gaskets and seals are used in every engine to keep engine oil contained inside the engine s lubrication system Oil consumption almost always occurs as a result of oil leaking out of its normal location after a gasket or seal has failed Even a relatively small internal or external oil leak can cause the loss of a quart of oil over 1 000 miles of vehicle operation Keep in mind that gaskets and seals are designed and engineered to keep the engine oil confined to where it is supposed to be inside the engine This includes keeping oil out of the combustion chambers and cooling system Page 32 of 67 MLR Engines eBook 2013 Melior Inc Pinpointing External Leaks External leakage can be detected visually in most cases Usually external oil leaks from engine gaskets or seals are the easiest to find The quantity of the leakage can affect how easily the leak source can be visually detected Oil leakage can be so slight that the
23. can tools use an electronic storage device to store software programs which must be updated periodically for new models and for changes to service information The screen displays the instructions and menus which are commanded through a keyboard or with buttons Current scan tools can receive and display data and can also send serial data messages to the PCM This two way communication is referred to as bi directional Data the scan tool receives include DTCs that have been set by a vehicle s PCM as well as live data from the serial stream with values for the many engine sensors and other system sensors sometimes referred to as parameters Scan tools can clear the trouble codes from the PCM s active memory and many will identify and provide information about the codes or the codes can be looked up in the service information Most scan tools can make a recording of a vehicle s data stream over a period of time that can then be analyzed frame by frame to help in identifying intermittent or rapidly occurring problems For more details on the scanner tool visit the web course MLR Engines at www todaysclass com The Importance of Mechanical Systems Often diagnosing a vehicle that has a DTC is not very difficult if you use the proper tools along with the service manual Other times what appears to be a problem with an input device or an output may really be a problem with a related circuit The problem could also be in a mecha
24. d be performed to locate the concern Here s a real world example of this process A regular customer brings you a 1994 Buick Century with a 3100 V6 VIN M engine The odometer in this vehicle shows 65 000 miles This customer states that within the last month the vehicle has suddenly began consuming oil at a rate of a quart every 500 miles Your shop has serviced this vehicle regularly so you have the vehicle s service history As a part of the information gathering process you find GM TSB 87 60 03 while researching manufacturer s technical service bulletins This technical service bulletin identifies lower intake manifold gaskets as being a potential cause for your customer s concern The bulletin also describes how to verify the customer complaint and even gives part numbers for updated gaskets that should be used in making the repair Keep in mind that your customer s vehicle still needs to be properly diagnosed The TSB in this example tells you how to perform the diagnosis to either confirm or rule out failed intake manifold gaskets as being the cause of the customer complaint Preliminary Engine Inspection Even after determining a diagnostic path or direction a preliminary inspection of the engine should be performed This may reveal other areas that need service or that may be contributing to the customer complaint Preliminary checks should include a visual inspection and confirmation Your inspection should include listening for
25. d on the compression stroke fuel can enter the crankcase by blowing by worn cylinder bores worn pistons or worn or broken HA piston rings Compression and cylinder leakage tests will provide valuable clues to determine if worn cylinder bores pistons or rings are responsible for excessive oil consumption High Mileage Engines High mileage engines that consume excessive amounts of oil often have multiple problems In many cases diagnosis of high mileage oil burning engines will reveal that the entire engine assembly is worn If any part of the engine is repaired in an attempt to reduce oil consumption the repair could place additional strain on another part of the engine Therefore high mileage engines are best completely reconditioned the first time Partial reconditioning may actually increase oil consumption Diagnosing Oil Pressure Problems Along with oil consumption problems the next most common lubrication system problems relate to engine oil pressure flow and volume The three most common oil pressure problems are as follows e Low oil pressure which can be indicated by low oil pressure gauge readings if the vehicle has an oil pressure gauge or an oil pressure indicator light coming on while the engine is running Abnormal engine noises knocks rattles ticks or other mechanical noise may also be noticeable e High oil pressure which can be indicated by high or excessive oil pressure gauge reading
26. d service procedures detailing component and fastener removal or installation sequence and fastener torque should be followed to the letter A generic overview of the valve seal replacement process is as follows Disconnect the negative battery cable Remove the engine accessories necessary for valve cover removal Remove the valve cover s oe NS Remove the valve train components e g rocker arms camshafts necessary to gain access to the valve springs Remove the spark plugs Insert an air hose adapter into the spark plug opening for the cylinder being serviced Connect the shop air hose to the adapter and pressurize the cylinder Use a valve spring compressor to compress the valve spring ee ee Note There are as many different designs of valve spring compressors as there are valvetrain designs Be sure to use the right compressor for the engine you re working on to minimize the possibility of injury or damage 10 Remove the valve locks retainers and spring See image below 11 Note A magnet will be handy here to remove and capture the valve locks Be careful not to drop them once they have been removed 12 Remove the old valve stem seal 13 Inspect the valve locks valve lock grooves and the valve stem and tip for signs of wear or damage 14 Inspect the valve springs for squareness and signs of wear or damage Measure their free height To do this stand all of the springs on a flat surface next to each oth
27. d small holes called valve guides are machined into it to position the valves The valves act as gates When open they let air and fuel into the cylinder and exhaust gas out When closed they seal the pressure of compression in the combustion chamber The valves close against machined surfaces in the combustion chamber ports called valve seats On overhead cam engines like the one pictured here the head also houses the camshaft The assembly together with other valve train components and the intake and exhaust manifolds is referred to as the top end Between the head and the block a head gasket seals the combustion chambers and water and oil passages Chapter 2 Engine Classifications Engines can be classified in many different ways according to their design characteristics and operation These differences can affect the methods of maintenance and repair Some ways engines can be classified are e Operational design four stroke two stroke rotary etc e Number of cylinders four five six eight 12 etc Page 4 of 67 MLR Engines eBook 2013 Melior Inc e Arrangement of cylinders V type inline etc e Displacement 3 8 liter 3800 cubic centimeters 350 cubic inches etc e Number of valves and valve train type overhead cam pushrod 24 valve etc e Fuel type gasoline diesel propane etc e Cooling system air or liquid Operational Design The Four Stroke Cycle Otto Cycle A stroke is o
28. d used in diagnosing all automotive systems A systematic approach will save time and ensure that the proper repairs are made Verifying the Customer s Concern Effective communication between the customer service writer and technician is essential for efficient and satisfactory repairs To begin with you must know the correct or normal operation of the system and verify that the customer concern is a deviation from normal operation You need to know what where when and the magnitude of the complaint This may necessitate a road test Try to have the vehicle owner driver ride along during the road test The owner driver can assist in identifying the source of any problems Remember that you will not always be able to verify or even identify each and every customer concern CAUTION e Always check engine oil and coolant levels prior to running the engine or road testing e Safety first when road testing NEVER drive in an unsafe manner when attempting to identify a problem Verify operation of the instrument panel engine warning indicators for correct operation and indicators that relate to customer concerns Verify engine gauge operation Engine gauges provide valuable information on the operating condition of the engine Oil pressure temperature charging system and fuel gauges are some of the most common types of gauges used on modern vehicles The method of gauge operation varies widely between manufacturers Oil pressure gau
29. e been used for many years in small engine applications such as outboard boat engines motorcycles ultralight aircraft chainsaws and lawn equipment etc Some two stroke engine automobiles have been imported to the U S and many medium and heavy duty diesel applications are currently equipped with two stroke engines Unfortunately the light weight and simplicity come at a price Conventional two stroke gasoline engines produce higher exhaust emissions and yield lower fuel economy than a comparable four stroke engine This is largely due to the burning of the oil in the combustion chamber and leakage of unburned fuel inherent in the engine s design The causes of this will be clearer when we examine the operation of the engine Nevertheless the two stroke engine has received renewed interest in recent years as innovations and advancements in fuel injection materials and engine management systems develop These engines have a pressurized lubrication system fuel injectors and superchargers that compress the intake air similar to a two stroke diesel engine The Two Stroke Cycle We ll begin the explanation of the two stroke cycle with the firing of the spark plug which occurs before every downstroke As the piston moves down delivering power the intake and exhaust ports are both covered At the same time the downward movement of the piston is pressurizing the crankcase with the next air fuel charge which was drawn into the crankcase th
30. e engine During engine operation some combustion gases leak past or blow by the piston rings and into the crankcase If the gases are not vented moisture sludge and acids will build up along with unwanted crankcase pressure The accumulation of these harmful gases can shorten the life of the engine and cause oil leaks These gases also contain the harmful emissions we have discussed and are a source of air pollution The PCV system removes blow by gases from the crankcase and routes them back into the combustion chamber where they can be burned instead of venting them to the atmosphere The PCV system was the first emission control device used on automobiles In a PCV system fresh air from the air cleaner is supplied to the crankcase where it mixes with the blow by gases from the combustion process The mixture of fresh air and blow by gases passes through the PCV valve and into the intake system to be burned in the engine Most PCV systems use a mechanical valve to control flow rate while others use an oil separator assembly The PCV valve s spring tension is designed specifically for each unique engine application The spring tension controls the flow rate of crankcase vapors into the engine preventing pressure buildup EGR FILTERED AIR a AIR INTAKE J INTAKE MANIFOLD NCRANKCASE BLOW BY GASES KEY TO PCV SYSTEM SEEM FILTERED AIA Ramee eLow BY GASES za b FILTERED AIR BLOW BY
31. e engine cooling system Inspect the cooling system by first checking coolant level and condition Inspect and test the radiator pressure cap coolant recovery tank and heater core and hoses on 4 a ET a 4 fy ie R Belt Tensioner Engine Cooling System Thermostat Top View Thermostat Diagnosing Leaks in a Cooling System There are several methods used to diagnose leaks in a cooling system Often the first test is a visual inspection Start by looking for a busted radiator or heater hose Next look at the water pump for leakage If a leak is visible there is no need to use other methods Page 42 of 67 MLR Engines eBook 2013 Melior Inc Pressure Testing Sometimes a small leak can be located using a pressure tester A pressure tester allows the entire cooling system to be tested at one time Radiator caps normally will have a pressure stamped on top Pumping the system to the recommended pressure and allowing the vehicle to sit for 10 15 minutes will normally help pinpoint a coolant leak For example if the radiator cap is stamped 15 lbs apply 15 lbs of pressure If after 10 minutes the pressure is holding at around 12 Ibs the system may not have a leak If the pressure drops there is a cooling system leak If the leak cannot be pinpointed externally this could be an indication of an internal coolant leak such as a head gasket or heater core leak Testing with Coolant System Dye Some coolin
32. e noticeable at slow engine speeds This is because the oil pressure leaks off past the loose bearing Slow engine speeds can compound this because the oil pump turns too slowly to overcome this leakage and maintain the proper pressure At higher engine speeds enough oil is pumped to overcome the leak and increase the oil pressure A sharp knock or a dull thud sound and low oil pressure together indicate worn connecting rod or main bearings Diagnosing oil pressure problems will be discussed in the next section Timing Chain Rattle or Slap Some engines use timing chains A rattle sound coming from the front of the engine is usually the result of a loose or stretched timing chain The chain will sometimes slap the timing cover or chain guide when the throttle is snapped Page 15 of 67 MLR Engines eBook 2013 Melior Inc Valvetrain Noise Excess clearance between valvetrain components sometimes produces a clicking or clattering sound that comes from high in the engine This sound has a higher frequency than a bearing knock With some engine designs extremely loose timing chains a Re Dat any of these points rocker arm can sometimes wear through the timing cover and cause an oil congas leak If the timing cover contains coolant passages between the W nolge water pump and the block 20R and 22R four cylinder Toyota engines for example a loose chain can wear through these passages as well An internal coolant l
33. e sure to observe the condition of the engine oil while it is being checked or drained during the oil change Oil that appears thin or watery and that has a strong fuel odor is a sign of fuel entering the crankcase A ruptured fuel pump diaphragm on a carbureted vehicle is a common cause for this Any condition that can cause excessively rich fuel mixtures could potentially cause fuel contamination of the engine oil as well The cause of the contamination needs to be diagnosed and repaired Oil that appears milky is a sign of coolant entering the crankcase If this is found the cause of the coolant contamination needs to be diagnosed and repaired as well Page 38 of 67 MLR Engines eBook 2013 Melior Inc If a low or abnormally high oil pressure condition is still indicated after the oil and filter have been changed test the oil pressure with a test gauge as per the vehicle manufacturer s published procedure and compare the test readings with manufacturer s published specifications Measuring oil pressure with a test gauge after changing the oil and filter will quickly provide diagnostic direction If the oil pressure test results are within manufacturer s specifications using a test gauge but the vehicle s oil pressure gauge or light reads abnormally follow the vehicle manufacturer s published procedure for testing the oil pressure light or gauge sending unit and circuit Pressure Indications Abnormally hig
34. eak will cause coolant and engine oil to mix Causes of excessive clearance can include worn valvetrain components a worn camshaft lobe a bent pushrod or misadjustment of valve clearance in the case of manually adjustable valves Valvetrain wear occurs with age and mileage Abnormal wear can be a sign of a lubrication system problem such as insufficient or dirty oil or clogged oil passages Keep in mind that replacement of worn components without correcting the lubrication problem may result in a repeat failure and comeback Non Engine Related Sounds If the noise occurs only when changing gears or going into or out of gear the engine itself may not be the problem The engine mounts transmission torque converter flexplate or clutch should be checked for wear or breakage Unit 2 ENGINE COMPONENTS INSPECTION AND REPAIR Chapter 1 Engine Components Cylinder Head Function and Construction As stated earlier in this course the cylinder head s main job is to contain the rapid increases in combustion chamber temperature and pressure that occur when the air fuel mixture ignites In addition the overhead valve cylinder head provides the mounting point for the parts that actuate the valves as well as for the intake and exhaust manifolds Combustion Chamber Spark Plug Hole Po or Page 16 of 67 MLR Engines eBook 2013 Melior Inc Exhaust Valve Valves Guides amp Seats Intake and exhau
35. ement instead of reconditioning Once the cylinder head is off and the external bolt on parts have been removed the gasket sealing surfaces must be thoroughly cleaned Be sure to clean all gasket surfaces especially the head gasket surface and the manifold surfaces Any gasket material left on the head surface will cause a leak when the engine is reassembled The head gasket surface on the cylinder block deck should be cleaned as well Note Use a gasket scraper to remove debris and gasket residue from gasket mating surfaces as previously discussed Cleaning gasket surfaces with surface conditioning disks is NOT recommended by vehicle manufacturers Cylinder Head Inspection and Reinstallation Knowing the specific customer complaint as discussed earlier can help you find what you re looking for when inspecting the cylinder head For example cooling system concerns like overheating and loss of engine coolant can in many cases be traced to a warped or cracked cylinder head Oil consumption complaints can sometimes be traced to worn valves and guides Misfire and power loss complaints are sometimes caused by burned valves that cannot keep the pressure of combustion confined to the inside of the cylinder In addition you may find that in some cases that replacing cracked worn or high mileage cylinder heads with new or reconditioned heads makes the most economic sense for the vehicle owner Warpage Check Check the head gasket surface fo
36. en the engine is shut down oil drains from the top of the cylinder head back to the crankcase During this time oil can leak past worn out or split valve seals and worn valve guides onto the backs of closed valves or into any cylinder where a valve is open Page 35 of 67 MLR Engines eBook 2013 Melior Inc Pinpointing valve guide and seal leaks can be difficult One sign of potential valve guide or valve seal leakage would be heavy blue smoke coming from the tailpipe immediately after the vehicle is started The volume of smoke will slowly taper off as the engine runs The smoke volume tapers off for two reasons As the engine warms the valves and guides expand slightly This reduces the amount of oil being pulled into the cylinders Also as the catalytic converter comes up to light off temperature it begins to consume the oil smoke before it exits the tailpipe Visible smoke on deceleration is another potential sign but again this may not be seen with a modern engine Worn valves guides and seals may cause oil residue in the form of carbon to build up on the backs of the valves Intake valves run cooler and are more susceptible to this Exhaust valves run hotter and may not have any or as much carbon buildup This buildup can be seen in some cases using a borescope to view the back of the valve via the intake port Borescopes are used for inspection work where the area to be inspected is inaccessible by other mea
37. er They should stand the same height and should stand squarely If there is any discrepancy in their height or if any of the springs do not stand squarely replace all of the springs Note The tension of each valve spring can be tested using a special gauge Extensive testing of valve springs is generally not cost effective In most cases it is cheaper to replace questionable valve springs than it is to test them particularly in a high mileage engine 15 Inspect the top of the valve guide for signs of wear or damage 16 Install a new valve seal Note Use caution to not nick cut chip or otherwise damage the new valve seal during installation Page 20 of 67 MLR Engines eBook 2013 Melior Inc 17 Reinstall the valve spring retainer and locks Note Once the valve spring retainer and locks have been reinstalled use a brass or plastic faced non marring hammer to LIGHTLY tap the tip of the valve stem BEFORE releasing air pressure from the cylinder Tap ONLY THE TIP of the valve stem NOT the valve spring retainer Tap lightly but hard enough to move the valve off of its seat You should hear a quick pop when the valve has moved caused by air pressure momentarily escaping the cylinder This is done to make sure that the valve locks are properly installed and seated Incorrectly secured or damaged valve locks will cause major engine damage when the affected valve falls into the cylinder and collides with the moving piston
38. erature This causes an exhaust emissions problem especially oxides of nitrogen that has limited their production in recent years In liquid cooled engines often called water cooled a pump circulates coolant though cavities and passages called water jackets around the cylinders and combustion chambers A thermostat keeps the engine at the optimum operating temperature by controlling the coolant flow between the engine and the radiator where the heat is given off to the air passing through it The coolant is normally a mixture of 50 water and 50 antifreeze The antifreeze provides protection against freezing boiling and rust and corrosion and provides lubrication and seal conditioning for the water pump Cooling system operation and service is covered in the Today s Class HVAC course From this point on this course will deal with gasoline powered liquid cooled four stroke piston engines Page 10 of 67 MLR Engines eBook 2013 Melior Inc Chapter 3 Mechanical Diagnostics Engine mechanical problems can have many causes Component wear is both normal and inevitable Anything with moving parts will wear with prolonged operation This wear can occur sooner than expected if an engine is abused or is improperly maintained Sealing gaskets can split or leak internal engine parts such as piston rings bearings and valvetrain components can wear and intake and exhaust valves can burn just to note a few common examples T
39. f current that was flowing through the primary induces the pulse of high voltage at a very low current in the secondary Little current is needed it is high voltage that s required to create a spark capable of jumping the spark plug gap and igniting the air fuel mixture Contact Point Systems Secondary terminal Primary positive terminal Primary negalive Secondary terminal winding Primary winding Ignition Coil The switching device must turn on and off very rapidly since it must interrupt the circuit to produce each spark In years past electromechanical contact points breaker points located in the distributor were used for this The points opened to trigger the firing of the coil It s helpful in understanding later ignition systems to examine how these early systems work As the distributor shaft rotates cam lobes on it open the points to interrupt the circuit and spring tension closes them to energize the primary winding again called dwell time A capacitor called a condenser is used to minimize arcing across the points Contact point systems require periodic adjustment and replacement and have performance shortcomings by today s standards but they work These systems were used for over 60 years but by 1975 most vehicles produced used electronic switching to fire the coil Contact points can still be found in electromechanical relays and solenoids Modern Systems Dwell adju
40. f the cylinder head and the cylinder wall in between if there is any cylinder wall exposed at TDC Many things such as the design and shape of the combustion chamber compression ratio fuel properties engine temperature and other factors can affect combustion in an engine Page 43 of 67 MLR Engines eBook 2013 Melior Inc Compression Ratio In an earlier section we said that the compression ratio is the volume of Bom tae Dare CONE enon re reo Compression Ratio of 8 1 the cylinder including the combustion chamber with the piston at BDC compared to the volume at TDC In the animation below you can see that the volume of the cylinder at BDC is eight times as large as its volume at TDC for a compression ratio of 8 1 If the total volume of the cylinder is 480cc with the piston at BDC what will the volume be with the piston at TDC Calculate your answer and then watch the animation to find out A higher compression ratio can increase the power and fuel economy of an engine but it also increases exhaust emissions and the temperature in the combustion chambers Higher compression engines require a fuel with a higher octane rating anti knock rating Abnormal Combustion Sometimes conditions that cause abnormal combustion occur The result is a loss of power engine noise and possibly engine damage Abnormal combustion typically takes one of two general forms pre ignition or spark knock Pre ignition Pre igniti
41. g system leaks are very difficult to pinpoint In this event using cooling system dye may be the best option Always use the dye according to manufacturer directions and always ensure the dye you are using is compatible with the coolant of the vehicle A UV dye will emit a bright green or orange color where it is escaping from the vehicle Using a UV dye will requires allowing the vehicle to cool and pouring the dye into the cooling system After test driving the vehicle return to the shop place on a lift and recheck for coolant leaks Bleeding Air from a Cooling System After repair a cooling system it may be necessary to bleed air from the system There are several different procedures depending on the manufacturer A vehicle with air trapped in the cooling system may overheat or the heater may not properly warm the passenger compartment in the winter In some cases air becomes trapped when a radiator hose or heater core is located higher in the vehicle that the radiator fill cap In this event the vehicle will have a coolant bleed port located in the system higher than the radiator When changing coolant or repairing a cooling system always follow manufacturer instructions for removing air or the engine may overheat causing severe damage Unit 4 COMBUSTION AND IGNITION SYSTEMS Chapter 1 Characteristics of Combustion The combustion chamber is the area over the piston when it is at TDC It is formed by the top of the piston the bottom o
42. ges Most vehicles come equipped with an oil warning light The problem with an oil warning light is that the light will not come on until the oil pressure has dropped to an extremely low point An oil pressure gauge is an electrical gauge that has a needle that only tells the operator whether there is oil pressure Oil pressure is critical to the operation of the engine For that reason most technicians prefer to use a mechanical oil gauge to verify oil pressure Temperature Gauge An engine that is overheating will soon develop major problems Overheating can be caused by low coolant stuck thermostat blown head gasket inoperative coolant fan or more severe engine problems such as cracked block or cylinder head If the temperature gauge reads hot verify that the coolant fans are operating and that the system is full of coolant Depending on the model and year of the vehicle there are different methods of testing the temperature gauge If the gauge is not reading on an older model vehicle mid to late 70s disconnect and ground the temperature sending unit wire at the sending unit If the gauge reads HOT the electrical circuit is normal If on a later model the temperature gauge does not read properly try grounding the temperature sending unit wire at the sending unit This should make the unit read COLD If with a cold vehicle the temperature starts out cold and slowly moves to hot as the engine warms up this may indicate an engine problem such as a st
43. h oil pressure as measured by a test gauge after changing to the correct oil and filter is generally caused by a stuck oil pressure relief valve Note Vehicle manufacturer s published service information should be consulted for diagnosis and repair of a high oil pressure condition Abnormally low oil pressure as measured by a test gauge after changing to the correct oil and filter indicates an engine mechanical problem If the engine is knocking or mechanically noisy engine damage has probably already occurred When oil pressure and flow are restricted inside an engine the resulting engine damage almost always happens before the gauge or warning light indicates a problem In many cases the circuit controlling the oil pressure warning lamp is designed not to turn the lamp on until the actual oil pressure is less than 4 5 PSI 27 6 34 5 kPa Further diagnosis of low oil pressure and mechanical noise usually requires oil pan removal and a thorough inspection of the oil pump oil pump pickup and engine bearings High Mileage Engines High mileage engines with low oil pressure and mechanical noise often have multiple problems In many cases further diagnosis will reveal that the entire engine assembly is worn Repair attempts made upon worn engines can sometimes compound problems Installing a new oil pump in a worn engine may increase the oil pressure slightly for a short time but it does nothing to reverse the wear that has
44. he camshaft s movement up to the rocker arms which rock to open the valves On these engines the cam acts on a valve lifter which in turn acts on a pushrod to move the rocker arm and open the valve Rocker Arm Pushrod Valve Spring Valve Seal Valve Guide Exhaust Valve Valve Seat Lifter or Tappet y Camshaft a Different engine designs may use different valvetrain designs some of which may not have all of the components previously listed Each valve must open and close at exactly the right time relative to the position of each piston This is accomplished through the camshaft and cam drive which will be covered later in this course Valve and Spring Retention Valve Springs are used to close each valve tightly against its seat as Valve Stem Keepers the closing side of the cam lobe passes the valve s actuating Spring ie mechanism These valve springs are held in place by a spring oc retainer Two valve keepers are used to lock the valve stem to the Valve Seal Valve Guide spring retainer as shown here The O ring and Valve Seal shown in the graphic are used to prevent engine oil from getting into the combustion chambers via the valve guide The O ring keeps oil that collects on top of the spring retainer from running down the valve stem The seal shown on top of the valve guide serves a similar purpose Page 18 of 67 MLR Engines eBook 2013 Melior Inc To remove the valve
45. he graph for friction Engine RPM horsepower represents the horsepower used to overcome the internal resistance in the engine Page 45 of 67 MLR Engines eBook 2013 Melior Inc Chapter 2 Ignition Systems Ignition Systems Overview The ignition system must take the vehicle s system voltage of about 12 volts and transform it to a high voltage of up to 60 000 volts to create sparks that jump the gap between the electrodes in each spark plug It must do this hundreds of times a second and at precisely the right time for each cylinder under all operating conditions We know that the ignition system provides the spark to ignite the air fuel mixture but how does it do it First let s divide the ignition system into its two main sections the primary and secondary circuits The primary ignition circuit consists of the battery the ignition switch another switching device and any other parts of the system that operate at or near vehicle system voltage normally from about 12 6 volts to about 14 2 volts In fact all of the vehicle s electrical system that operates at this voltage can be referred to as the primary electrical system The secondary ignition circuit is the high voltage section and consists of the distributor cap and rotor DI systems spark plug wires and spark plugs Both the primary and secondary circuits must include a return path to ground Ignition Coil Another very important component in the ignition sy
46. he same cam lobe that they were removed from if they are to be reused Failure to do this will cause rapid cam lobe rocker arm and or cam follower wear e The contact surfaces of the lifters tappets are some of the highest friction points in an engine If a cam lobe is worn replace the cam and ALL lifters Never run used lifters on a new camshaft or new lifters on a used cam Rapid wear will result Valvetrain Reinstallation The following things are important to keep in mind during valvetrain reinstallation Mechanical and Hydraulic Lifters A small clearance has to be left between the valve and its actuating mechanism to allow for thermal expansion and wear Valves must always close and contact their seats completely A valve that does not close completely would rapidly burn away at the face and seat areas especially in the case of the exhaust valve Engines using mechanical lifters require periodic valve Valve body heck Ball check i valve i clearance lash adjustment Mechanical solid lifters are on of a fixed length The hydraulic lifter was designed to ensure that the rf Plunger valvetrain always operates with zero clearance leading valve Pushrod retainer to quieter operation and eliminating the need for periodic adjustment of valve clearance These lifters are designed to automatically adjust their lengths to maintain zero valvetrain clearance This length adjustment is accomplished using engine oil pres
47. ice as much in order to produce enough heat to ignite the fuel Compression ignition engines such as diesels must be designed heavier and stronger than spark ignition engines to withstand the compression and combustion produced in the cylinders These engines have steel sleeves pressed into their cylinder bores All diesel engines use fuel injectors to deliver the fuel to the combustion chambers at just the right time If the fuel were delivered along with the Piston air as in a gasoline engine the fuel would ignite prematurely The fuel pressure at the injectors must be very high to overcome the pressure in the combustion chambers created during the g Fuel injector compression stroke Keep in mind that with the mixture RU 7 port fuel injection systems on gasoline engines the fuel is injected outside the combustion chamber near the intake port and drawn into the cylinder on the intake stroke Intake Valve Induction Stroke Compression Stroke Power Stroke Exhaust Stroke Other significant differences between gasoline and diesel powered engines are the result of differences in the fuels they burn Diesel fuel is thicker heavier and less volatile than gasoline However there is more energy contained in a gallon of diesel fuel than in a gallon of gasoline While a gasoline engine can produce more power by weight than a diesel engine the diesel engine runs much leaner and provides better fuel efficiency by about one third
48. ice procedures detailing component and fastener removal or installation sequence and fastener torque should be followed to the letter Be sure to drain coolant and other necessary fluids as completely as possible prior to cylinder head removal to avoid spills If the head is to be resurfaced or reconditioned it should be partially disassembled once it has been removed from the engine Bolt on parts like the intake and exhaust manifolds thermostat housing rocker shaft or camshaft spark plugs glow plugs fuel injectors and the like should be removed at this time if they were not removed while pulling the head off Page 21 of 67 MLR Engines eBook 2013 Melior Inc Notes e When removing or reinstalling these parts follow manufacturer s specific published service information and instructions for the vehicle that you re working on e Manufacturer s specific service procedures detailing component and fastener removal or installation sequence and fastener torque should be followed to the letter Do not remove the valves and springs at this time This will be done during the inspection process If you break a bolt or strip threads on the cylinder head where bolt on parts attach during disassembly make note of this Don t try to extract a broken bolt or perform a thread repair on the cylinder head until after the head has been inspected thoroughly There s no sense in fixing a cylinder head that an inspection may show needs replac
49. inder may have 12 18 24 or 30 valves and a V 8 may have 16 24 32 or some other number of valves Pushrod Engines Pushrod engines those with the cam in the block are sometimes referred to as overhead valve engines to differentiate them from overhead cam engines but all modern automobile engines use overhead valves The term was originally used to distinguish the pushrod valve arrangement from engines that have the valves in the block a design now found only in antique cars and some small engines In pushrod engines the cam acts on a valve lifter which in turn acts on a pushrod to move the rocker arm and open the valve Fuel Type By far the most common fuels for the internal combustion engine are gasoline and diesel fuel however some fleet vehicles burn alternative fuels such as natural gas propane or liquefied petroleum gas LPG These engines are usually converted gasoline or diesel engines Cooling System Type Engines are either air cooled or liquid cooled Nearly all automobiles currently in production have liquid cooled engines Air cooled engines can be found in motorcycles lawn mowers and some automobiles Cooling fins cast on the outside of engine parts especially the cylinders and heads increase surface area and help dissipate heat into the air flowing around them Air cooled engines run at higher temperatures than liquid cooled engines under some conditions and they can t maintain as constant a temp
50. ion Developing higher compression would require using higher octane fuel However holding the intake valve open longer reduces the compression stroke The effect is a longer power stroke which allows more energy to be achieved from the expanding gases Hybrid Engine Service Hybrid engines are serviced in the same general way as any other engine However using the correct oil and following the recommended oil change intervals is critical Most hybrid engine cooling systems require special attention when servicing Mixing coolant can often cause premature failure of radiators and head gaskets Always following manufacture remediation when determining coolant service intervals and types of replacement coolant Unit 3 ENGINE LUBRICATION COOLING AND RELATED LEAKS Chapter 1 Lubrication and Oil Leaks All moving engine parts that have been discussed here must be lubricated which makes the engine s lubrication system a critical part of engine operation Lubricating oil helps carry away heat and reduces friction and wear between moving parts If a sufficient quantity of oil under pressure is not delivered to vital engine parts such as rod and main bearing journals the engine would seize within the first few minutes of operation The Lubrication System A supply of oil is maintained in the oil sump at the bottom of the oil pan Submerged in this oil is a pickup tube covered with a screen The pickup tube leads to the oil pump which is dri
51. ir Injection Page 55 of 67 MLR Engines eBook 2013 Melior Inc A vehicle scan tool is required to check the status of vehicle monitors Some inexpensive scan tools do not have the capability to run a check of monitors Diagnostic System Checks Most service manual sections have systems checks that verify proper operation of the system These lead you on an organized approach to diagnostics The system checks help narrow down the possible causes of a system fault Once you have evaluated the situation you should have enough information to perform a bulletin search Other service information includes videos newsletters and troubleshooting hints in the service manual Using any stored DTCs follow the designated DTC chart to make an effective diagnosis and repair Select the symptom from the symptom tables and follow the diagnostic paths or suggestions to narrow down the possible causes and test for the root cause You should develop a plan for diagnostics using wiring diagrams theory of operation and your experience You may need to call technical assistance for more information Repair and Verification After a cause has been isolated make the repairs and validate proper operation Verify that the symptom has been corrected This may involve performing system checks or road testing the vehicle Verify the correction under the conditions noted by the customer Common Diagnostic Resources and Tools There are many re
52. ir fuel mixture e When fuel requirements decrease the injector ON time decreases producing a leaner mixture INJ DRIVER CYL 1 INJ DRIVER CYL 3 INJ DRIVER CYL 5 INJ DRIVER CYL 2 INJ DRIVER CYL 4 INJ DRIVER CYL 6 Typical Fuel Injector Circuit A fuel injector is an electromagnetic device The precision mechanical components are controlled by means of the solenoid in the injector and the solenoid is energized through vent an injector driver in the PCM The injector is triggered based on ignition reference pulses Coil Windings Armature Strainer Armature Spring PCM Although engine RPM determines when an injector opens the PCM determines how long to leave the injector open based on its readings of coolant temperature engine load throttle position and oxygen sensor O2 voltage Page 62 of 67 MLR Engines eBook 2013 Melior Inc The PCM driver circuit controls the ON time of the solenoid by Volts providing a ground When the injector driver opens the circuit to a ee Narrow the solenoid turns it off return spring tension pushes the ball or pintle onto its seat and shuts off fuel flow Because of the wide variety of air fuel systems on vehicles it is ka 12 Control Pulse imperative to consult the service information for the vehicle on m Wide which you are working before you attempt diagnosis and repairs CAUTION Always follow all
53. ive which uses a Timing Belt along with Pulleys and or Sprockets Belts are lighter and quieter than timing chains They also do not require engine oil lubrication As with overhead cam chain drives tensioners can be mechanical or hydraulic Guide pulleys are used rather than guide rails where needed Gear Drive which uses two or more Gears meshed directly Very few modern gasoline engines use direct gear drive between the cam and crank though some diesel truck and equipment engines still do Systems Overview Engines are complex machines that rely on several systems for their operation These systems include air fuel delivery ignition cooling lubrication exhaust emission controls and the computer system It is important to understand each system when diagnosing performance problems as these systems work together to provide efficient operation Each of these systems will be covered in depth later in this course Page 19 of 67 MLR Engines eBook 2013 Melior Inc Chapter 2 Inspection and Repair Cylinder Head Diagnosis and Repair On Car Valve Seal Replacement Many technicians will replace valve seals on high mileage engines in response to customer complaints of oil consumption and or visible smoke out of the tailpipe This is a short term repair in many cases Replacing the valve seals does not recondition the cylinder head and may not solve the oil consumption problem long term Note Manufacturer s specific publishe
54. kets Leaks are revealed by submerging the head in a tank of water or spraying it with soapy water Bubbles indicate leakage There are other ways to look for cracks A magnetic particle crack detector can be used on cast iron heads and a spray on dye penetrant that glows under ultraviolet light can be used on aluminum heads Crack detection is another job that most shops will sublet out to an automotive machine shop Valve and Guide Inspection The contact area of each valve where it rests on the valve seat is Valve Seat eat Angie called the face The valve face and seat are what actually seal the intake and exhaust ports when the valves are closed Both of these areas are precision machined 2 ere Angle 1 2 1 interference angle As well as providing a seal this valve face valve seat contact area also allows the heat of combustion to be transferred from the valve to the seat and water jacket while the valve is closed The high temperatures found in the combustion chamber would rapidly burn away the face and seat of any valve that does not make solid contact when closed especially in the case of an exhaust valve Valve Face The valvetrain is designed to rotate every valve slightly with each opening and closing event This is done to help equalize valve seat and face wear All valve faces and seats should be closely inspected The contact areas should be true and shiny The actual width of each face and seat can be
55. l be ending its compression stroke while the other will be ending its exhaust stroke and this method is called a waste spark system as the spark on the exhaust stroke does nothing On this one coil per plug system the coils are mounted on the valve covers Note the fuel rail located above the valve cover information for the vehicle on which you are working before you attempt diagnosis and repairs Note Use care working with the secondary circuit with the engine running While getting a shock from the high voltage is not normally injurious to healthy persons it is not pleasant Far more common are injuries caused by the involuntary reflex reaction to being shocked banged head lacerated hand or worse Engine Diagnostic Tests Engine diagnosis can be complex No matter how good the tune up an engine with a burnt valve will still misfire A vacuum leak can cause a rough idle and a timing belt that has jumped will always cause a loss of power For that reason any good tune up begins with determining the engine condition Several diagnostic tests can be performed to determine overall engine condition The specific test you will perform depends on the type problem the vehicle is experiencing For example a vehicle with a DTC diagnostic trouble code P0300 is experiencing a random cylinder misfire A vehicle with a DTC P0301 is experiencing a misfire on cylinder number one For these two DTCs your diagnosis process may be different O
56. l carbon removers can help soften tough deposits CAUTION Be careful not to gouge or scratch machined surfaces when cleaning aluminum heads Page 23 of 67 MLR Engines eBook 2013 Melior Inc Inspect the valve springs for squareness and signs of wear or damage Measure their free height To do this stand all of the springs on a flat surface next to each other They should stand the same height and should stand squarely If there is any discrepancy in their height or if any of the springs do not stand squarely replace all of the springs Note The tension of each valve spring can be tested using a special gauge Extensive testing of valve springs is generally not cost effective In most cases it is cheaper to replace questionable valve springs than it is to test them particularly in a high mileage engine Next the valve seats along with the area under the valves should be checked visually for damage or cracks If any of the valve seats appear damaged loose or pitted they should be replaced or repaired This is another job that most shops will sublet out to an automotive machine shop As noted previously there still may be cracks that are not visible even under close inspection It is therefore recommended that the cylinder head be pressure tested before any further inspection or machine work is performed Pressure testing requires sealing up all the water openings in the head and applying regulated air pressure to the cooling jac
57. limate conditions had caused a severe smog problem in the Los Angeles Basin By the mid 1960s the first emission control systems were being installed on all new cars sold in the U S and in 1967 the Clean Air Act was amended to include standards for automotive emissions The Environmental Protection Agency EPA develops and enforces environmental regulations Within a few years fuel economy standards were introduced as well in the Corporate Average Fuel Economy CAFE standards With increasingly stringent emissions regulations that began in 1993 much has been done to reduce vehicle emissions and emissions from an average vehicle today are less than 5 of a 1960 model However the increase in the number of vehicles on the road causes emissions to continue to be a concern Emissions from the exhaust crankcase and fuel evaporation are controlled Standards are set primarily with regard to three emissions hydrocarbons HC carbon monoxide CO and various oxides of nitrogen NOx Hydrocarbons HC Hydrocarbons are simply unburned fuel During combustion hydrogen and carbon are converted in combination with oxygen but not all of the molecules are converted Some pass through the combustion chamber and come out of the engine as unburned fuel known as hydrocarbons High levels of hydrocarbons are often related to problems in the ignition system Some causes of high HC are misfire improper timing low compression vacuum leaks or incorrect ai
58. llow it to idle Once the engine is running use the Propane Enrichment Tool to feed propane into the valve covers one at a time via the PCV grommet or oil cap If there is a manifold gasket leak the propane will be pulled into the cylinders by manifold vacuum This in turn will cause the Carbon Monoxide and Hydrocarbon readings on the Exhaust Gas Analyzer to change Some manifold gasket leaks will be large enough to cause the engine to smooth out or change speed once the propane is applied at idle If the manifold gasket leak is very small this test may not be conclusive Valve Guides and Seals The vacuum created inside the cylinder by the intake stroke is applied directly to the intake valve stem If the valve stems or valve guides are worn or if the valve stem seals are defective oil can be drawn into the intake runner at the cylinder intake port Worn exhaust valves guides or seals can cause oil consumption as well At a point between the exhaust stroke and the intake stroke the exhaust valve will still be open though the piston has reached the top of its stroke At this point the Venturi effect of the exhaust gases moving out of the engine can cause a vacuum in the combustion chamber This vacuum is momentary but can be strong enough to pull oil through a worn exhaust valve guide around the valve stem Once siphoned past the exhaust valve the oil will be burned by the hot exhaust gases in the exhaust ports and manifold Wh
59. llow that can t be mistaken for anything else This may be the best way to pinpoint small leaks that occur only during special circumstances such a driving vibrations road shock or flexing of components and lines Page 33 of 67 MLR Engines eBook 2013 Melior Inc When you use the dye follow the dye kit directions Larger leaks will show up within a short time once the dye has been added to the engine oil and the engine has been run For smaller less obvious leaks you may have to add the dye to the oil and have the customer return in a few days or even weeks To see the leak put on the UV glasses that come with the UV light Next turn on the UV light shine it on the area you suspect to see leaking and look for a trail of dye from the bottom of the engine upwards Once the trail is visible under the light follow it up to the highest point to find the source of the leak Pinpointing Internal Leaks Internal leakage can be very difficult to detect In fact internal leakage will often continue without being detected Modern engines run at high internal engine temperatures and are also equipped with very efficient catalytic converters These can mask internal oil leaks by causing any telltale smoke to be burned before it has a chance to make itself visible by coming out of the tailpipe Oil can leak or be drawn into the induction system via several different paths Some of the more common causes of internal leakage
60. lution of the crankshaft which provides more power and smoother running The cylinders can be arranged in a number of ways The three most common cylinder configurations are inline V type and opposed Engines with even numbers of cylinders have pairs of companion cylinders in which the pistons move up and down together When one of the pistons is on its power stroke the other one will be on its intake stroke Likewise when one piston is on its exhaust stroke its running mate will be on its compression stroke Look for the companion cylinders in the animations here Inline Engines Inline engines have all their cylinders in a straight row This is a common arrangement for four cylinder engines and inline six cylinder engines are still produced Many years ago inline eight cylinder engines were produced but there are several problems associated with an engine of that length V Type Engines V type engines have two cylinder banks a left bank and a right bank at an angle to one another such that when viewed from the front or rear the block forms the shape of a V As with all matters of automotive service left and right are referenced from the vantage point of someone sitting in the vehicle V 6 and V 8 engines are common while a few V 10 and V 12 engines are produced The V 6 has several advantages over inline 6 engines The V type is more space and weight efficient Two connecting rods from opposing banks share one crank pin
61. mal Gaskets vacuum hoses vacuum operated systems and accessories that operate on vacuum may leak causing lower manifold vacuum When the throttle plate is closed at idle the vacuum in the manifold is greatest When the throttle plate is open and the manifold is exposed to atmospheric pressure vacuum is lower Using a vacuum gauge to check manifold vacuum is a quick and easy way to test an engine It is a good indicator of the engine s ability to run efficiently Typical engine vacuum will produce a steady reading of between 15 and 22 inches of mercury inches Hg with the engine at normal operating temperatures idling and in drive Vacuum also changes with load so if accessories are operated while monitoring vacuum the readings will change Vacuum readings will also vary between engines One reason is differences in compression ratios If an engine has higher compression it will have 1 to 2 inches Hg higher vacuum Altitude also affects vacuum For every 1 000 feet above sea level vacuum will be lower by 1 inch Hg Some engines that use a high lift camshaft or have considerable valve overlap will produce a slightly lower erratic needle reading on a vacuum gauge Some areas that can be diagnosed using vacuum readings include e Engine components i e valves valve guides and springs piston rings e Manifold leaks e Valve timing e Restricted exhaust system In addition low manifold vacuum can significantly affect the computer co
62. measured and compared to manufacturer s specifications Pitted or obviously worn seats and faces should be reconditioned Worn valves and seats can sometimes be resurfaced by cutting or grinding using special tools but if they are severely worn replacement may be required Severely burnt valves will have a section of the face burned or melted away and should be replaced Page 24 of 67 MLR Engines eBook 2013 Melior Inc Valve guides will always wear keyhole style in a direction that is perpendicular or sideways to the length of the cylinder head This wear occurs because the ages AA valvetrain loads the valve in this direction as the valve is opened and closed Check for valve and guide wear by reinserting the valve into its corresponding guide Hold the valve in its approximate open position a quarter inch 6 5 mm off of the valve seat With the valve in this position wiggle the valve back and forth crosswise at a 90 degree angle to the head If you can feel movement or play the guide or valve stem is worn A dial indicator can be used to measure the actual amount of play Set up the dial indicator to contact the edge of the valve when it is in its normal open position so that it will indicate crosswise movement As noted earlier this should be a quarter inch 6 5 mm off of the valve seat With the valve in this position wiggle the valve back and forth crosswise at a 90 degree angle to the head Note any indic
63. n to top dead center TDC before removing the old timing belt CAUTION Timing must still be verified before trying to start the engine Most engines have timing marks that will assist with aligning the cam and crankshaft gears Perform Common Fastener and Thread Repair Removing broken bolts can be time consuming and challenging Any time a bolt breaks there are few options for removal If the bolt is broken flat drilling and using an easy out may be the best option Try drilling a hole in the center of the bolt Install the easy out and try turning out slowly DO NOT BREAK the easy out An easy out is made of very hard material and very difficult to drill If after installing an easy out you discover the easy out alone will not remove the broken bolt try heating the area around the bolt Use caution not to overheat aluminum If neither the easy out nor heating the area around the bolt works it may be necessary to over drill the broken bolt and tap to a larger size if the area and situation permits If this is not an acceptable repair option using new thread inserts may be the only option left Repairing External Threads Repairing external threads is normally much easier than repairing internal threads In most cases replacing bolts is the best option However there are tools made that can be used to repair external threads Hybrid Engine Service and Operation As an automotive technician you should familiarize yourself with the safety and
64. nagement EVAP Vent Valve Transmission Shift Solenoids Transmssion Pressure Control Sclenaid a a p k a a a E a m E E d E E E b b Of E Accmlerator Pedal Position Sengor Note Not all sensors are used in any one system Some such as the TP sensor are used in all systems But others such as the cruise control switch or the accelerator pedal position sensor are used only for certain applications On Board Diagnostics and OBDII Requirements All vehicles weighing less than 14 000 Ibs that are produced after 1996 are required to be equipped with an OBDII diagnostic system The OBDII system is required to monitor every system that effects engine emission The primary goal of OBDII is to ensure the vehicle operates as cleanly as possible for the entire life of the vehicle A secondary concern was a lack of standardization within the automotive industry Before OBDII each manufacturer had used different scan tools fault codes and connectors OBDII systems are required to use the same OBDII connector and Diagnostic Trouble Code DTCs for all emission related codes However manufacturers still use some DTCs that are brand specific OBDII expanded the number and scope of systems being monitored and required more specific monitoring of emissions OBDII systems will only set a DTC when pre programed conditions are met DTCs can be broken down into two categories Type A and Type B Note A drive cycle i
65. ne movement of the piston either down from Top Dead Center TDC to Bottom Dead Center BDC or up from BDC to TDC The term stroke also refers to the physical distance between these two points One stroke of the piston moves the crankshaft through one half of a revolution Almost all engines on the road today operate on a cycle of four piston strokes The strokes are the intake stroke compression stroke power stroke and the exhaust stroke This cycle turns the crankshaft through two revolutions and then the process begins again Let s put our simple engine into motion to see what happens in a cylinder during this four stroke cycle We will begin with the intake stroke Intake Stroke The process begins with the intake stroke The piston moves down from top dead center TDC to bottom dead center BDC The movement of the piston creates a partial vacuum drawing air and fuel into the cylinder through the open intake valve The ideal air fuel mixture for performance economy and emission control is 14 7 parts air to 1 part fuel On Throttle Body fuel Injection TBI systems and old carbureted systems fuel is carried in the air stream through an intake manifold and into the intake port On Multiport Fuel Injection MFI systems each cylinder has its own injector which allows fuel to be injected into the port with more precision and uniformity than possible with Throttle Body systems During thi
66. nes use a number of Cylinder Head T cylinders to produce sufficient power to drive the wheels but operate much like a small engine in many ways Let s look at one cylinder of an engine to see how the main parts work per Counterweight together a ee Connecting Rod Engine Block The block is a heavy metal casting usually cast iron or aluminum which holds the lower parts of the engine together and in place The block assembly consists of the block crankshaft main bearings and caps connecting rods pistons and other components and is referred to as the bottom end The block may also house the camshaft oil pump and other parts The block is machined with passages for oil circulation called oil galleries not shown and for coolant circulation called water jackets JN LG Crankshat i seh 238 i EA ey m oi P awe Pi g PaA T Page 2 of 67 MLR Engines eBook 2013 Melior Inc Cylinders The cylinders are round holes or bores machined into the block for the pistons to travel up and down in Pistons Combustion pressure acts upon the tops of the pistons in the cylinders forcing them downward Usually made of aluminum the pistons transmit the downward force to the connecting rods The top of the piston s travel is called Top Dead Center TDC and the bottom of a piston s travel is called Bottom Dead Center BDC Piston Rings Rings are installed in grooves around the pistons to form a seal bet
67. ngine and write down the reading with the engine idling e Snap the throttle quickly the idea is not to increase engine speed but get a large amount of air into the cylinder e Running compression at idle should be about cranking compression Snap throttle compression should be around 80 of cranking compression Page 50 of 67 MLR Engines eBook 2013 Melior Inc A running compression test checks the engine s ability to breathe If the running compression is low air did not make it into the engine This can possibly mean a worn intake cam lobe If the running compression is high above 80 air did not escape the engine possibility a worn exhaust cam lobe It is always a good idea to test more than one cylinder when performing a running compression test and compare the reading If all cylinders fail check the timing chain or belt for misalignment Check for Vacuum Leaks A vacuum leak can cause several engine drivability concerns A severe vacuum leak will cause the catalytic converter to run hotter than normal A less severe vacuum leak can cause a rough unstable idle Most manufacturers now use a smoke machine to check for manifold vacuum leaks It is not uncommon for a vehicle with a manifold vacuum leak to display a DTC P0171 or P0172 Oil Pressure Test A vehicle with low oil pressure may be worn to the point that a tune up is a waste of time and money Never depend on just the oil pressure gauge or light when diagnosing a
68. nical system Don t forget that under all the electronics there is still a basic engine The engine management system assumes that all of the powertrain mechanical systems are functioning properly Several items might cause conditions that could be blamed on the engine management system Examples include e Low compression Page 57 of 67 MLR Engines eBook 2013 Melior Inc e Vacuum leaks e Exhaust system restrictions e Problems with fuel delivery including fuel pump fuel filter fuel lines or bad fuel e Worn ignition system components bad wires fouled spark plugs etc e Incorrect basic ignition timing e Cooling system malfunctions e Transmission transaxle faults Manifold Vacuum and Testing The intake stroke of the pistons creates a vacuum in the manifold Vacuum is any pressure lower than atmospheric pressure The strength of the vacuum created affects the distribution of air and fuel to the cylinders Higher vacuum means better distribution An engine s ability to form and hold a vacuum is directly related to its ability to form and hold compression When an engine loses the ability to create vacuum performance suffers The amount of vacuum formed in the manifold depends on several factors First the cylinders must be sealed If a cylinder has low compression or high leakage it may not produce sufficient vacuum to draw in the air fuel mixture Second the manifold must be sealed or vacuum will be lower than nor
69. nock or pre ignition Most late model vehicles are equipped with a PCM controlled Knock Sensor KS system Engine mounted knock sensors are used to detect vibrations caused by knock When a knock is detected the PCM retards spark timing to eliminate the knock Torque and Horsepower Torque is turning or twisting force The power developed in an engine s cylinders is converted into a turning force by the crankshaft which delivers this torque to the drive train where it is transmitted to the wheels Torque is measured in pounds feet lb ft although it is often casually expressed as foot pounds which is actually a measure of work In the metric system torque is given in Newton meters Nm or kilogram meters kg m Horsepower is the rate at which torque is produced One horsepower was designated many years ago as the amount of work required to lift 550 pounds one foot in one second The torque and horsepower an engine can deliver vary with engine speed In the example of a typical Forge performance graph shown below note that maximum torque is developed at low to moderate 2 RPM while brake horsepower the power Be bad 5 available at the end of the crankshaft continues to p horsapower 4 rise into the high RPM range At higher RPM the n i l torque and horsepower curves begin to drop due to difficulties in the engine s breathing at the 500 1000 1500 2000 2500 3000 3500 4000 higher speeds The line on t
70. ns They are usually fitted with a magnifying device and a way to illuminate the area being inspected Port fuel injectors can be removed on engines so equipped to get a glimpse of the back of the valve as well Another method of inspecting the back of the valve with a borescope is to go in via the spark plug hole and rotate the engine carefully by hand until the intake valve is open Valve and guide inspection and measurement which requires cylinder head disassembly is often the only way to determine valve and guide wear Compression and cylinder leakage tests will not pinpoint worn valve guides or leaking valve seals Many technicians will replace valve seals on high mileage engines in response to customer complaints of oil consumption and or visible smoke out of the tailpipe This is a short term repair in many cases If the valve stems and guides are worn excessive play between the two surfaces will wear new positive type valve seals out quickly Cylinder Bores and Piston Rings As shown and discussed earlier in this section oil can enter the combustion chamber by blowing by worn cylinder bores worn pistons or worn or broken piston rings Page 36 of 67 MLR Engines eBook 2013 Melior Inc As the piston travels downward on the intake stroke oil can enter the combustion chamber by blowing by worn cylinder bores worn pistons or worn or broken piston rings As the piston travels upwar
71. nt and fastener removal or installation sequence and fastener torque should be followed to the letter e Carefully inspect both the head and the block Make sure that there is no head or block damage that will affect the sealing of the gasket The cylinder head and block gasket surfaces should be clean and free of all old gasket materials and sealer e Head bolt holes in the block should be cleaned with a tap or thread chaser After cleaning use compressed air to blow out any loose debris e lf head bolts are to be reused they should be cleaned on a wire wheel Torque to yield head bolts cannot be reused and must be replaced e Follow manufacturer s specific published service procedures and recommendations for applying lubricant or sealant to head bolts Don t apply lubricant or sealant unless one or the other is specifically called for Valvetrain Diagnosis and Repair Inspecting Overhead Camshaft Valvetrain Components Overhead camshaft valvetrain components are easily inspected as the cylinder head is being disassembled for service In many cases a close visual inspection will suffice Cam lobe measurements can be taken if there s a doubt about lobe wear but visual comparison of multiple lobes should make it easy to note one or more Gr that are worn Visually inspect cam lobes and rocker arms followers for signs of scoring or excessive wear at their three contact points Cam lobes and rocker arms followers
72. ntrolled fuel system in turn affecting performance This is because the engine management system uses a manifold absolute pressure MAP sensor to influence spark timing and fuel control Page 58 of 67 MLR Engines eBook 2013 Melior Inc In reference to vacuum and pressure keep in mind that a vacuum still has a certain amount of pressure It is simply lower than atmospheric pressure Normal atmospheric pressure at sea level is 14 7 pounds per square inch psi but most standard pressure gauges such as a tire gauge assign atmospheric pressure a value of 0 Some pressure specs are actually expressed in psig indicating pounds per square inch gauge to distinguish them from absolute pressure Higher air pressure will always flow into an area of lower pressure if it is permitted Readings Average steady readings between 15 22 Hg normal readings for a 60 V6 engine may be lower i e 12 16 inches Hg Low but steady between 12 and 15 inches Hg Needle fluctuates or drops between 1 and 2 inches Hg at idle Irregular needle drop between 1 and 2 inches Hg at idle Normal at idle speed but excessive vibrations at higher rom Possible Causes Normal Leaking around piston rings late ignition timing or late valve timing Burned or leaking valve or spark plug in one of the cylinders is not firing Sticking Valve intermittent spark plug misfire or rich or lean air fuel mixture Weak v
73. o come into wide use on vehicles will be Controller Area Networks CAN which can transmit data at 1Mb or 1 000 000 bits per second The PCM controls many devices related to engine operation In order to make operating decisions the PCM depends on information from a network of sensors switches and other modules located throughout the vehicle The data from these devices are considered inputs to the PCM Page 53 of 67 MLR Engines eBook 2013 Melior Inc OPERATING PARAMETERS SENSED AIC High Side Pressure ANG On or Oi Camshaft Position Cruise Control Switch On or Off EGR Signal Engine Coolant Temperature ECT Engine Crank Signal Fuel Pump Vollage Ignition Reference Crankehatt Position Engine Speed APH intake Air Tamperature IAT Knock Sensor KS Manilo Absolule Pressure MAP Mass Alr Flow MAF Oxygen Sensor O25 Post Converter Oxygen Sensor Park Neutral Switch P N Position Power Steering Pressure PSPS Sysiem Voliage Throttle Posstion TP Transmission Gear Position Vehicle Speed VSS Fuel Tank Pressure Sensor SYSTEMS CONTROLLED Aur Conditioning Compressor Relay Air Management EVAP Canister Purge Cruise Control Diagnostics Malfunction indicator Light MIL Data Output DLC Fuel Pump Relay Exhaust Gas Racirculaton EGR Fuel Injector s Idle Air Control LAG Ignition Control IC Transmission Gonvertar Clutch TCC Shift Light Engane Torque Ma
74. on occurs when the air fuel mixture self ignites during the compression stroke before the spark plug fires This condition has the effect of trying to force the piston back down the cylinder before it reaches TDC Pre ignition is the result of a hot spot in the combustion chamber that prematurely ignites the mixture The early combustion creates abnormally high cylinder pressures and temperatures that the engine cannot withstand Causes of pre ignition include hot spark plugs incorrect heat range excessive accumulation of glowing carbon deposits in the combustion chamber overheated exhaust valves and cooling system malfunctions Pre ignition is more prevalent during high speed and load conditions Engine damage resulting from pre ignition can include melted spark plug electrodes melted scuffed pistons ring damage and distorted valve heads Spark Knock Pinging Spark knock or pinging is caused when the flame front initiated by the spark plug collides with an undesired flame front The undesired flame front starts when part of the unburned air fuel mixture is compressed to a pressure and temperature that exceeds the self ignition limit causing it to spontaneously ignite The fuel explodes too quickly rather than burning smoothly This condition is also referred to as detonation Spark knock makes a pinging noise and occurs mostly under high load and low to medium speed conditions Page 44 of
75. pection should also be made for hairline cracks in the combustion chambers ports face sides and top of the head Be sure to examine the spark plug glow plug and or injector holes for damaged threads and cracks Look closely around the head bolt holes for cracks and evidence of coolant leakage Many cracks can be very difficult to see Keep in mind that there may be cracks that aren t visible even under close scrutiny If a crack is found don t do anything else to the head until it is determined if the crack is repairable In most cases a cracked cylinder head will need to be replaced If no cracks are found after a close visual inspection the valves and springs can be disassembled Make sure to mark and record the location of each valve as it is removed The tips of the valve stems may have become mushroomed or enlarged from being pounded by the rocker arms This can happen after an engine has been run for long periods of time with excessive valve clearance Any valve that has a mushroomed stem should have the mushrooming filed off before the valve is removed CAUTION Don t try to drive mushroomed valves out with a hammer and punch this will damage the valve guide After the valves are out carefully clean the carbon from the ports and valve guides A wire brush in an electric drill can be used on cast iron heads aluminum heads should be cleaned by hand using a gasket scraper or carbon removal tool Chemica
76. r Inc Coolant To cover all possible vehicle conditions the coolant must have a low freezing point a high boiling point and the ability to hold a lot of heat Water is an effective heat carrier but its freezing and boiling points must be enhanced to make it a suitable coolant A mixture of water and antifreeze ethylene glycol is used for this Most manufacturers recommend a 50 50 mix which yields protection against freezing to 35 degrees F 37 C and raises the boiling point to 223 degrees F 106 C Antifreeze also contains an additive package to inhibit corrosion and lubricate the water pump The coolant must not boil because when a fluid boils it cannot absorb any more heat Its temperature will remain the same even though the temperature of the surrounding metal may continue to rise Since coolant temperature can sometimes rise as high as 275 degrees F 135 C more must be done to raise the coolant s boiling point The boiling point is further raised by pressurizing the system typically to about 15 pounds per square inch psi This will raise the boiling point another 45 degrees F 25 C The relationships between heat pressure and changes of state liquid to gas and back will be examined in detail in the Refrigeration Systems Overview As the coolant in the system heats up pressure is created The pressure cap on the radiator serves as a pressure relief valve If the pressure exceeds the cap s rating it will push
77. r fuel ratio Carbon Monoxide CO Carbon monoxide is partially burned fuel and the product of incomplete combustion As previously stated carbon is one of the elements that make up the fuel burned in the engine together with oxygen If the combustion were complete carbon emissions would come out of the engine in the form of carbon dioxide or CO 2 which is harmless to humans Carbon monoxide on the other hand is a potentially lethal gas that is also odorless and colorless High carbon monoxide emissions can be caused by an Page 64 of 67 MLR Engines eBook 2013 Melior Inc excessively rich fuel mixture low idle speed a restricted air filter faulty PCV system or a faulty fuel delivery system Oxides of Nitrogen NOx Nitrogen makes up about 78 of the air going into an engine Under extremely high temperatures it combines with oxygen to form oxides of nitrogen NOx NOx when exposed to sunlight and combined with unburned hydrocarbons creates the visible air pollutant known as smog Smog is a problem in many heavily populated areas of the world Oxides of nitrogen can also combine with other molecules in the atmosphere to form compounds contained in acid rain NOx is created when combustion chamber temperatures are too high above approximately 2500 F Common causes of excessive NOx include inoperative EGR cooling system malfunction lean air fuel ratios etc Catalytic Converter The catalytic converter reduce
78. r warpage using a precision straightedge and a set of thin feeler gauges Check the head gasket surface lengthwise and crosswise in several places Gasket Sealing Surface Precision Straightedge The black lines indicate strait edge positions for warpage check Page 22 of 67 MLR Engines eBook 2013 Melior Inc As a general guideline warpage lengthwise should not measure more than 003 in 0 076 mm for a three cylinder V6 head 004 in 0 102 mm for a four cylinder or V8 head or 006 in 0 152 mm fora Straight six head When measuring side to side the maximum allowable limit for warpage for any head is 002 in 05 mm Note Manufacturer s specific specifications for warpage should be followed to the letter The figures given here are general guidelines If a cylinder head is warped it should be straightened before any other machine work is done This is typically a job that most shops will sublet out to an automotive machine shop Some heads can be milled shaved down to make the gasket sealing surfaces flat and true again Overhead cam cylinder heads are sometimes straightened by bolting the head down over shims to a Straightening fixture The head and fixture are then heated in an oven to 450 to 500 deg F 230 to 260 deg C for three to six hours The assembly is then cooled slowly to de stress the metal Disassembly and Visual Inspection for Cracks After checking for warpage a close visual ins
79. rod journal Page 8 of 67 MLR Engines eBook 2013 Melior Inc Opposed Engines Opposed engines have cylinders that face each other from opposite sides of the crankshaft This arrangement is sometimes called a boxer or pancake engine because the cylinders lay flat giving the engine a low profile This makes it suitable for rear and mid engine applications and this type of engine has been used in Porsches Volkswagens air cooled and Subarus Slant A slant arrangement has also been used This arrangement is a variation on the inline design and some manufacturers have used it to lower the hood line It sets in the engine compartment at a slant and may resemble half of a V type engine A few high end automakers have produced engines with 16 cylinders ina W arrangement but with a price of around one million dollars you are unlikely to see one ina typical shop The W arrangement is done to conserve space W Type Q CO Re Re D Top Cylinders are assigned numbers by the manufacturer for reference The numbering system varies by manufacturer Sometimes the numbers are stamped into the intake manifold The firing order is the sequence in which the spark plugs fire and is usually different from the order of the cylinder numbers The firing order may also be stamped on the intake manifold but both sets of numbers are available in the service information for the vehicle The firing order will var
80. rod or from a piston pin In other cases the rod bearing and piston pin produce two different types of noise Page 14 of 67 MLR Engines eBook 2013 Melior Inc Note Distinguishing between a wrist pin knock and a rod bearing knock is not critical at this point in the diagnosis Repairing either component requires engine disassembly and further inspection Piston Slap Piston slap is a knocking sound caused by a piston rocking in a worn cylinder bore and contacting the cylinder wall Piston slap sounds much like a wrist pin knock However unlike a wrist pin knock a piston slap generally quiets down as the engine warms up and the piston expands Sometimes killing fuel or spark to one cylinder at a time will temporarily make the piston slap get louder or change its sound Correction of the piston slap also requires engine disassembly and measurement Main Bearing Knock A main bearing knock sounds more like a dull thud than a knock A main bearing knock comes from lower in the engine The knock is loudest when the engine is under a moderate to heavy load The cause is usually worn crankshaft main journals and or worn main bearings allowing the crankshaft itself to flex under load This in turn makes the crankshaft move up and down inside the cylinder block Main Bearing Knock In addition to audible noise loose connecting rod bearings or main bearings will usually cause low oil pressure This low pressure will be mor
81. rough the air fuel inlet and around the reed valve This pressure forces the reed valve to close As the piston continues downward it uncovers the exhaust port Remaining combustion pressure begins to blow the spent gas out the port Spark plug Combustion chamber Exhaust port Reed valve Air fuel Mixture Intake port saami Ajir fuel Inlet Page 6 of 67 MLR Engines eBook 2013 Melior Inc Further downward movement uncovers the intake port as well and both ports are open for an instant as the pressurized air fuel charge from the crankcase enters the cylinder The incoming air fuel purges the remaining exhaust gas from the cylinder As the piston travels upward again it covers the intake and exhaust ports so compression can begin At the same time the piston s movement creates a vacuum in the crankcase opening the reed valve again and drawing in the next air fuel charge Diesel Engines The diesel engine is another reciprocating piston design Diesel engines in passenger cars and light trucks operate on the four stroke cycle but they have important differences from the gasoline engines we have discussed The most significant difference is the way in which diesel engines ignite the fuel Rather than using a spark to start the combustion a diesel engine uses the heat produced by compression of the air in the cylinder Diesel engines must compress the air much more than a gasoline engine does about tw
82. s if the vehicle has an oil pressure gauge or an obviously swollen oil filter housing e A malfunctioning oil pressure indicator light or gauge circuit which can indicate that there is an oil pressure problem when the system is actually functioning normally As simple as it sounds checking the engine oil level and sie sists condition should be where diagnosis begins The dipstick should _ lt q read full when checked and the oil should be clean and of the R y j i i correct viscosity as specified by the engine manufacturer Ls Page 37 of 67 MLR Engines eBook 2013 Melior Inc Changing Oil and Testing Pressure As vehicle technology has evolved engine oils have evolved from regular mineral engine oils to synthetic blend or full synthetic motor oils Caution should be taken to use correct engine oil Using the wrong type or grade motor oil can affect engine performance and shorten engine life Newer engines use lower tension piston rings because of this using heaver engine oil than recommended by the manufacturer can cause premature engine damage If there is any doubt whatsoever about the condition of the engine oil or oil filter change it before going any further in your diagnosis Even if further diagnosis reveals major mechanical problems four or five quarts of the correct viscosity oil and a clean correct oil filter are a very cheap way of eliminating potential variables during the diagnostic process B
83. s a knocking sound The rod bearing knock sounds loudest at the lower part of the engine and it may change at a particular engine speed or load When the engine is cold the oil is thicker The knock may be quieter or even absent as a result As the engine warms up the oil thins out This may make the knock more noticeable Sometimes killing fuel or spark to one cylinder at a time while the knock is at its loudest will temporarily quiet the knock or make the knock sound change This will enable you to identify which rod bearing is knocking This test may not be conclusive when rod bearings are extremely worn CAUTION Always use factory approved methods when interrupting or stopping spark or fuel ona running engine for safety and to minimize the chance of engine or component damage During a road test the rod bearing knock may be speed sensitive becoming quieter as engine speed and load is increased or decreased When rod bearing noise becomes more severe it will tend to lose this speed sensitivity Piston Pin Knock Excessive clearance at the other small end of the connecting rod can cause a knock as well A knock at the piston wrist pin sounds somewhat like a rod bearing knock but will be located much higher in the engine than the rod knock It also may or may not be sensitive to changes in engine speed load or temperature In some cases the location of the knock may be the only way to determine if it is coming from a
84. s a test drive that duplicates a short freeway trip that closely simulates a daily drive to work While the vehicle is being driven the PCM is running a series of tests to ensure the emission control system is operating properly Type A DTC e Emission related e Will turn on the malfunction indicator light MIL after one drive cycle or when the condition usually a misfire is severe enough to damage the catalytic converter Page 54 of 67 MLR Engines eBook 2013 Melior Inc e Type A trouble codes will store freeze frame date after one drive cycle Type B DTC e Emission related e Type B DTC will set a pending code after the first failed drive cycle However the MIL will not illuminate until the 2nd failed drive cycle e Some Type B pending DTC codes are cleared after one successful drive cycle e Type B DTC will illuminate the MIL after two driven cycles where the same failure occurred e Type B DTCs will not store freeze frame date until the 2nd drive cycle the failure occurred on most vehicles When a failure occurs that will set a DTC and an orange light will illuminate in the instrument cluster The light will usually say check engine or service engine soon OBDII systems have a system of readiness monitors that run when certain driving conditions are met When DTCs have been repaired or the system needs resetting the system may not pass an emissions test because all monitored driving conditions have not been met
85. s all three exhaust insutaTion NSULATION emissions Converters contain small amounts of rhodium palladium and platinum When heated these elements act as catalysts and convert the exhaust gases the HC CO and NOx into the harmless substances of water H20 carbon dioxide CO2 and nitrogen N Emission Subsystems EVAP System Hydrocarbons are released from fuel in vapor form In the past fuel tanks had vented caps and HC was released into the atmosphere Hydrocarbons escaped when the fuel tank was being filled or even when the car was in operation Hydrocarbon vapors are referred to as evaporative emissions To reduce HC emissions systems have since been developed to recover the vapors that evaporate from the fuel An EVAP system is used to collect fuel ee vent vapor from the fuel tank These vapors evar emssions VZ ZZZ are then stored in a canister filled with Ain FLow oimecnon activated carbon The EVAP system wy EAr PUNCE SOLENOID EV NORMALLY CLOSED WV allows the vapors to be drawn from the hid canister into the engine and burned i N J during certain operating conditions This is called purging since the vapors are purged from the canister NNS Evan EMISSION PRESSURE CONTROL LVE WITH INTERNAL ORIFIC FUEL TANK ROLL OVER VALVE Page 65 of 67 MLR Engines eBook 2013 Melior Inc PCV A positive crankcase ventilation PCV system reduces crankcase emissions and protects th
86. s produced since 1996 are required to comply with OBDII standards Controller Area Network CAN bus is one of five 5 protocols used in OBDII equipped vehicles The primary on board communication network between the microprocessors and electronic control modules ECMs now use CAN communication protocol In a CAN system redundant wiring is greatly reduced because various input and outputs are shared between modules There are several different CAN bus configurations Always check service manuals to determine what particular system you are diagnosing Page 51 of 67 MLR Engines eBook 2013 Melior Inc Chapter 1 Computer Systems and OBDII Computer Systems On late model vehicles the Powertrain Control Module PCM or in some cases the Vehicle Control Module VCM operates the entire engine management system A PCM is a computer that controls the engine and transmission and stores Diagnostic Trouble Codes DTC for these systems A VCM also controls and stores codes for other systems such as the antilock brake system Computer is a broad term A computer is any device that can take input information and perform a set of instructions then generate a specific output For example a computer may receive input from a keyboard such as typing numbers calculate a formula with those numbers and then output a result on a screen The computer also may activate a motor turn on a switch or perform just about any kind of engine management
87. s stroke the exhaust valve remains closed Power Stroke This is what it s all about As the piston nears TDC with both valves closed the compressed air fuel mixture is ignited Combustion occurs resulting in a tremendous pressure increase that pushes the piston back down the cylinder This is the power or working stroke The intake and exhaust valves remain closed In an idling engine this happens in each cylinder about five times a second and running at 4 000 RPM it happens over 30 times a second Compression Stroke After the piston passes BDC the compression stroke begins The intake valve closes and the mixture in the cylinder is compressed by the piston as it moves upward again to TDC The intake and exhaust valves are both closed during this stroke so the pressure and temperature of the air fuel mixture rises A typical compression ratio for a gasoline engine might be 9 1 The compression ratio is the volume of the cylinder including the combustion chamber with the piston at BDC compared to the volume with the piston at TDC The crankshaft has now made one revolution Exhaust Stroke Now the spent gasses must be removed from the cylinder to make room for the next air fuel charge The exhaust stroke begins as the piston nears BDC The exhaust valve opens and the piston moves upward again pushing the burned exhaust gases out of the cylinder The intake valve remains clo
88. s that can fall into the spark plug holes e Set the throttle plates to wide open position e Install the compression gauge into the cylinder you are testing If testing all cylinders most manufacturers recommend starting at cylinder number one e Crank the engine for approximately 5 6 seconds and record the highest reading Be sure and crank each cylinder approximately the same amount of time e Allcylinders should read approximately the same As a rule of thumb they should all be within 10 of each other For instance for an engine with a cylinder that has its highest reading at 150 Ibs no other cylinder reading should be less than 135 lbs If a cylinder s compression reading is lower than normal try adding a few squirts of clean motor oil and retesting If compression is now normal there is a good possibility that the engine has a worn or broken piston ring If compression remained low test for a burnt or bent valve In any event a basic tune up will not repair the problem Running Compression Test A running compression test or dynamic is run after a static compression test The steps are as follows e Put all the spark plugs back into the engine except for the cylinder you are going to test e Disable the ignition and fuel injector for the cylinder e Remove the Schrader valve from the compression gauge The test can be done with the Schrader valve in but it will need to be released every 4 5 compression strokes e Start the e
89. safety precautions and keep fuels away from sparks or flames Injector Pulse Width Modulation Exhaust System The exhaust system must collect the spent gas from each cylinder and route it to the rear of the vehicle for discharge to the air The major components of the exhaust system include e Exhaust manifold s e Exhaust pipes and seals e Catalytic converter s e Muffler s e Tailpipe s e Heat shields e Hangers clamps and hardware Exhaust systems have a major affect on airflow through engines Exhaust pipe diameters must be sufficient to allow the engine to expel exhaust gases at the proper rate with minimum backpressure If exhaust gases are not expelled effectively the air fuel charge to the cylinder will be diluted and engine performance will suffer If the diameter is too large the engine could run cooler increasing emissions levels Although exhaust system operation is simple the oo design is often more complex Exhaust manifolds must fit in cramped engine compartments without sharp bends that would restrict gas flow gum St NJ TAILPIPE while still leaving access for serviceability High a aa SSS T pressure pulses produced when the exhaust Oa eee valves open and close must also be muffled to KR KK Se reduce exhaust noise Baffles in mufflers minimize exhaust noise and catalytic converters contribute to noise reduction EXHAUST PIPE A major component in the exhaust system is the catalytic con
90. sed until the piston has almost reached TDC again At this point the engine has completed one full cycle and the crankshaft has rotated twice The entire process then repeats Page 5 of 67 MLR Engines eBook 2013 Melior Inc While the vast majority of automobile engines are gasoline powered four stroke reciprocating piston engines other engine designs have been developed and used in automobiles some quite successfully Additionally changing economic environmental and political conditions have created a demand to modify or retire this proven workhorse with new or re worked designs As materials and technologies improve and evolve some of these contenders may come into common use in automobiles Two Stroke Cycle Engines A two stroke cycle engine is another reciprocating piston design Every downstroke delivers power in this design and it has no valve train Instead in a conventional two stroke gasoline engine the air fuel and exhaust gas are managed by the piston as it covers and uncovers intake and exhaust ports in the side of the cylinder It also has no oil sump or pressurized oil delivery system because the crankcase is part of the fuel delivery system Instead the crankcase is lubricated by mixing a small amount of oil with the fuel Being able to deliver power with every down stroke and not having a heavy valve train means the two stroke engine can provide a lot of power for its size and weight Two stroke engines hav
91. service issues that are inherent when dealing with hybrid vehicles In a hybrid vehicle DC power provided by a battery pack is run through an inverter The inverter converts the DC voltage into regulated 3 phase AC voltage As a safety precaution hybrid vehicle high voltage wiring is bright orange When servicing or replacing a component that is in the high voltage electrical system the following steps are recommended e Remove the ignition key and place in a safe place like your pocket e Disconnect the 12 volt battery before disabling the high voltage batteries Page 30 of 67 MLR Engines eBook 2013 Melior Inc e Using insulated gloves access the high voltage battery pack e Remove the orange service plug and store it in a safe place e Wait 5 minutes before touching any high voltage wires Using a volt meter ensure that there are no charged high voltage electrical circuits Note Some manufacturers recommend placing electrical tape over high voltage orange electrical wires Hybrid Engines Engines used in hybrid vehicles are different than engines used in non hybrid vehicles Most hybrid engines operate using an Otto cycle The Otto cycle is only slightly different than the normally used Atkinson cycle The Otto cycle engine has a longer stroke than an Atkinson cycle engine To avoid the high compression that is normally produced by having a longer stroke the intake valve is held open longer resulting in lower compress
92. source is not apparent A leak could also be so massive that one entire section or even the whole engine is covered with oil To diagnose large leaks wash the engine off and run it in short cycles to prevent a flood of oil from covering a large area around the leak a second time Small leaks can be diagnosed by washing the leak area off letting it completely dry and coating it with a tracing powder to pinpoint an oil seep Aerosol foot powder available in any drug store can be used for this purpose Spray the general area of the leak with the foot powder The resulting white powder film will stick to the engine Then run the engine for a half hour or so in the shop or drive the vehicle fairly slowly in a parking lot or on a clean dry road Keep both vehicle speed and engine RPM slow as higher engine and vehicle speeds will tend to blow the powder off of areas where it was sprayed CAUTION Always check engine oil and coolant levels prior to running the engine or road testing Safety first when road testing NEVER drive in an unsafe manner when attempting to identify a problem Be sure to use approved exhaust ventilation equipment when operating a vehicle in an enclosed area UV Leak Dye Another way to pinpoint small difficult to trace oil leaks is by adding leak dye to the engine oil A UV ultraviolet light can then be used to find the location of the leak When viewed under the UV light the dye glows a bright greenish ye
93. sources available to the technician to help with diagnosis The following is a list of some resources Service Bulletins are currently available to technicians in several formats including CD ROM and paper Manufacturer s Internet Communication SystemsWith a subscription to the manufacturer s database you can perform a search of published bulletins via the Internet on a PC or laptop computer After a connection to the bulletin database is established the technician types in keywords that relate to the vehicle owners concern The system will display any bulletins that match the keywords Service Manuals provide information such as diagrams specifications diagnostic charts and procedures for each vehicle It contains many system checks It is an important tool and knowing how to find service manual information is essential to diagnosis and service of engine performance conditions The Onboard Diagnostic System Check is a critical step in diagnosis of engine performance conditions Locate this system check in the drivability or engine controls section of the service manual Service manuals may be available online and in paper format Many diagnostic tools can be used in troubleshooting engine performance problems Following is a list of common tools e Digital Volt Ohmmeter DVOM or multimeter is an essential automotive tool that functions as a voltmeter ammeter ohmmeter and more A high impedance unit is necessary for automotive use e
94. spring or to remove the valve from the cylinder head with the cylinder head off of the engine a tool called a valve spring compressor is used There are as many different designs of valve spring compressors as there are valvetrain designs but they generally fall into one of two categories On Car Valve Spring Compressor This valve spring compressor can be used without removing the cylinder head These are designed for replacing valve springs and or valve seals with the cylinder head on the car Compressed air is fed into the cylinder before the spring is removed to keep the valve from falling into the cylinder Off Car Valve Spring Compressor This valve spring compressor requires removing the cylinder head If a valve must be replaced for any reason the cylinder head must first be removed from the engine block Camshaft Drive Components The camshaft must open and close each valve at exactly the right time relative to piston position This is accomplished via the cam drive The camshaft is driven by the crankshaft via one of three methods Chain drive which uses a timing chain and sprockets Chains used on overhead cam engines typically use a chain tensioner and guide rails as shown here The tensioner can use an internal spring mechanical or engine oil pressure hydraulic to maintain chain tension Most chains used in cam in block engine designs do not use guide rails or tensioners because the chain length is much shorter Belt Dr
95. st valves open and close their respective ports Small holes called valve guides are machined into the ports to position the valves Valve guides are the bearings upon which the valves move Some engine designs use separate replaceable valve guides These are most often press fitted into the cylinder head Others use nothing more than a hole of the correct diameter machined into the head to guide the valve The valves close against precision machined areas or inserts in the combustion chamber ends of the ports called valve seats These are shown here in cutaway view As with the guides some engines use press fitted replaceable valve seats while others have the seat machined directly into the cylinder head a stem Pressed in valve guide Valve stem Integral clearance Cylinder a Pressed in WA Integral valve seat valve seat Page 17 of 67 MLR Engines eBook 2013 Melior Inc Valvetrain Construction Single Overhead Camshaft Engine The valvetrain consists of the valves camshaft 5 Camshaft and other associated parts OO m Bearing Rocker Arm Basic operation of the overhead camshaft Roller Follower valvetrain was discussed earlier in this course i aa Seal g Locks Hydrauli Lash Adjuste Spring Valve Guide Valve Seat Valve Pushrod Engine Engines with the camshaft located in the block are called pushrod engines because long pushrods are used to transmit t
96. stat that controls coolant circulation in the system Coolant is pumped through the engine where it absorbs the heat of combustion to the radiator where this heat is transferred to the atmosphere The radiator is a heat exchanger Hot coolant flows through tubes that are folded back and forth many times The tubes have many fins attached to provide more surface area with which to dissipate heat Air flowing around the tubes carries away the excess heat then the coolant returns to the engine to continue the process Let s begin at the water pump and follow the coolant flow through a typical system The pump sends the fluid to the engine block where it flows through passages around the cylinders The coolant then flows through the cylinder head and to the thermostat where it is directed back to the pump cold closed or to the radiator hot open To heat the passenger compartment another circuit is added to the cooling system This circuit pumps hot coolant from the cylinder head through a heater core in the dash and then back to the pump In this way heat can be obtained whether the thermostat is open or closed The heater core is another heat exchanger like a small radiator A blower fan blows air through the heater core and into the passenger compartment A heater control valve controls coolant flow through the heater core according to the temperature selected by the operator Page 40 of 67 MLR Engines eBook 2013 Melio
97. stem is the ignition coil The coil or coils is part of both the primary and secondary circuits The high voltage is produced here The coil is a step up transformer that produces high voltage pulses Aptly named it contains two coils of wire that are insulated from each other a primary winding and a secondary winding The outer primary winding contains hundreds of wraps of relatively large wire while the inner secondary winding contains thousands of wraps of much smaller wire The wires are insulated from each other so that current must flow through all of each coil The start of the secondary winding is connected to one end of the primary winding The primary winding receives vehicle system voltage or near to it and the secondary winding produces high voltage pulses that exit the center high tension terminal of the coil on their way to the spark plugs The high voltage pulses are created through electromagnetic induction and this is where the switching device comes into play Page 46 of 67 MLR Engines eBook 2013 Melior Inc Current flowing through the primary winding creates a strong magnetic field around the coil When the switching device interrupts the current flowing through the primary winding the magnetic field collapses across the secondary winding This induces a pulse of high voltage in the secondary Since the secondary winding has many more turns of smaller wire than the primary winding the moderate amount o
98. stment screw Contact points Rubbing block cam follower From negative side of coil Cam on Cond ondenser distributor storage capacitor Solid state electronic triggering and switching devices are now used an all automobiles produced but the principles used are very similar to those used in contact point systems These systems are much more accurate and provide better emissions fuel economy and performance than contact point systems could They can produce higher voltages and are more reliable with little or no maintenance needed Different manufacturers have used several different designs of electronic triggering and switching These systems use some type of signal generator on the distributor or crankshaft such as a timing disc i e trigger wheel and pickup coil in the distributor or a Hall effect pickup on the distributor or crankshaft On these systems movement of the timing disc generates a voltage signal in the pickup coil which is sent to a transistor in the control module or PCM to control switching Other engine sensor inputs may also be used Page 47 of 67 MLR Engines eBook 2013 Melior Inc DI Systems In DI systems the high voltage pulses from the coil are sent to the rotor at the top of the distributor shaft As the rotor turns the pulses are sent to the proper spark plug wires through the distributor cap Old distributor systems used weights on the distributor plate
99. sure along with simple valving inside the lifter itself Valve Lash Adjustment As stated earlier both hydraulic and mechanical valve train clearance must be set when the valve train is assembled Mechanical valve train clearance must also be maintained by periodic measurement and adjustment Hydraulic valve clearance will be automatically maintained making periodic maintenance unnecessary Page 28 of 67 MLR Engines eBook 2013 Melior Inc Methods for adjusting valve lash clearance vary depending on both engine design and the design of the valve lifter There are so many different vehicle designs engine and valvetrain configurations and other variables that it would be impossible to come up with a valid generic set of lash adjustment instructions Note Manufacturer s specific service procedures detailing component and fastener removal sequence lash adjustment and fastener torque should be followed to the letter Camshaft Drive Component Inspection Adjustment Replacement The timing chain and sprockets should be replaced as a set if the chain is stretched or the sprockets are worn past manufacturer s specifications Some timing chain sprockets have nylon or plastic teeth to reduce noise These can fatigue and break with heat and age When these teeth break they wind up in the oil pan Cleaning these pieces out should be a part of the timing chain replacement job as they can stop up the oil sump pickup screen Gears in a
100. sure to these places from the oil galleries Counterweights are formed onto the crankshaft to help prevent vibration These weights are added to offset the weight of the piston and connecting rod assemblies At the front of the crankshaft outside the engine front cover a heavy wheel containing a rubber vibration damper is installed Also called a harmonic balancer it often incorporates the crank drive belt pulley which powers belt driven accessories At the rear of the crankshaft a large flywheel is mounted The flywheel can serve several purposes a ring gear is mounted to its circumference to provide a means to start the engine It also connects the engine to the transmission Finally on vehicles with manual transmissions the flywheel is made very heavy to help smooth out power pulses from the engine this is accomplished by the torque converter on vehicles equipped with automatic transmissions Cylinder Head Like the engine block cylinder heads are usually cast from either iron or aluminum Most V type opposed and W type engines have two cylinder heads Inline engines have only one cylinder head The head bolts to the top of the block covering and enclosing the tops of the cylinders The head forms small pockets over the tops of the pistons called combustion chambers The spark plugs are threaded into holes in the head and protrude into the combustion chambers gasoline engines Intake ports and exhaust ports are cast into the head an
101. t far enough out of time while they are turning that the pistons will hit any open valves The result is valve valvetrain or piston damage Other engines use what is called a freewheeling design This means that the engine is designed with enough piston to valve clearance to keep these parts from colliding even if the crank and cam get out of time while they are turning Page 29 of 67 MLR Engines eBook 2013 Melior Inc Timing chain or belt replacement on some vehicles may require special tools Some belt pulleys gears or chain sprockets may be press fitted onto the camshaft crankshaft or auxiliary shaft Specific pullers and or installers may be required to service these items Note Manufacturer s specific service procedures detailing component and fastener removal sequence component inspection adjustment or replacement and fastener torque should be followed to the letter Timing Belt Replacement Timing belts should be replaced at routine service intervals depending on the manufacture and engine design Some timing belts may be need replacing at 60 000 miles Timing belt replacement procedures vary between vehicles and manufacturers In an interference type engine a broken timing belt can cause major damage to the valves and cylinder head In a non interference engine the piston will not come in contact with the valves even if the timing belt should break When replacing a timing belt it is recommended to set the pisto
102. take manifold for an MFI system does not carry fuel and can be tuned for either maximum torque or horsepower Since it carries only air itis referred to as a plenum Long air passages called runners that provide for increased low end and mid range torque are possible without the concern of fuel condensing on the manifold walls The fuel injector sprays a pulse of fuel and the air fuel entering the right cylinder around the open intake valve The plenum carries only air Fuel is delivered either above the throttle plate TBI or in the intake port nearer the intake valves MFI The fuel injector s are controlled by the PCM Many designs of fuel injectors are used but all have the same primary function When the injector nozzle opens and the pressurized fuel is injected an atomized air fuel mixture is provided to the engine The fuel further atomizes as it enters the combustion chamber Page 61 of 67 MLR Engines eBook 2013 Melior Inc Fuel Injector Fuel injectors are provided a continuous supply of pressurized fuel from the electric fuel pump An injector is a solenoid that energizes when grounded by the PCM to deliver pressurized fuel into the intake manifold or intake port The PCM controls fuel flow by pulse width modulation of the injector ON time The duration of this ON time is called the pulse width e When fuel requirements increase the injector ON time increases producing a richer a
103. ther common tests would be listening for a front engine noise or running compression tests using both static and running compression Not all tests are required however Determining that a tune up will most likely improve performance is a technician s responsibility Page 49 of 67 MLR Engines eBook 2013 Melior Inc An engine diagnosis test usually starts with plugging a scan tool into the DLC connector usually located under the dash on the driver s side If a DTC is present follow manufacturer diagnostic procedures to determine the cause of the problem Always remember that a DTC only provides a starting point for diagnosis A vehicle with a P0301 misfire on cylinder one does not mean that replacing the spark plug on cylinder one will repair the problem In most cases there is another problem that is causing the misfire Cranking Compression Test In the case of a misfire that does not go away at higher RPMs a compression test may be necessary A compression test can reveal important information about internal engine condition Remember an engine with low compression cannot be tuned up properly until the problem causing the faulty compression reading is repaired The step to perform a compression test is as follows e Warm the engine to normal operating temperature e Shut the engine off and disable the ignition system e Remove all spark plugs and label the ignition wire where necessary Make sure there are no loose material
104. uck thermostat coolant leak or other more serious problem Page 12 of 67 MLR Engines eBook 2013 Melior Inc CAUTION When a temperature gauges reads hot allow the engine to cool before removing the radiator cap Information Gathering In identifying and verifying the customer s concern you are actually gathering information from both the customer and from the vehicle itself This process of gathering information is an essential step in forming a diagnostic strategy that in turn will identify the cause of the customer concern Once you ve gathered information form the customer and the vehicle the next step is to research service information related to the owner driver s concern Service manual information and technical service bulletins TSBs should be searched and read to familiarize yourself with the system TSBs may also contain information on updated parts and service procedures related to your customer s concern Another part of information gathering even when dealing with engine mechanical issues is using a scan tool Stored Diagnostic Trouble Codes can provide useful information as can control module calibration or software identification numbers Ideally this step should be performed during the road test It should be done before researching service information Determine a Diagnostic Direction Based on the information that you ve gathered you now should be able to determine what diagnostic procedures shoul
105. unusual sounds looking for sources of fluid leaks and checking for unusual odors The vehicle service history can provide useful information as well Evaluating Engine Noise Unusual noises can be indicators of engine damage or wear Pinpointing and evaluating engine noise is a very difficult diagnostic job It is important to attempt to locate the area where the noise appears to be Page 13 of 67 MLR Engines eBook 2013 Melior Inc coming from before tearing the engine apart Noise is sometimes transmitted to other locations and can often be difficult to isolate Practice and experience will make this process easier over time A technicians stethoscope or probe can be helpful in successfully locating and evaluating engine noise The stethoscope can be moved around until the exact location of the noise is determined If a stethoscope is not available a long thin screwdriver or a piece of hose can sometimes be substituted CAUTION Use extreme caution when using a stethoscope or long screwdriver around electrical connections and moving parts Note that is would be impossible given the scope of this course to attempt to list every possible sound from every type of engine The following section is designed to show common causes of abnormal engine sounds Rod Knock A worn loose connecting rod bearing causes the big end of the rod to hammer on the rod journal of the crankshaft as the piston moves up and down This hammering make
106. vehicle with low oil pressure Always use a mechanical gauge to verify a low oil pressure reading However if oil pressure is low and there is a lot of engine noise coming from engine valve train an engine overhaul may be required to return the vehicle to normal operating condition Cooling System Before a vehicle can run properly the cooling system must be operating properly A vehicle that is running too cool will more than likely develop drivability concerns A cool running engine will usually not run as efficiently as a properly warmed engine If a vehicle is running too cool check to see if the engine thermostat is stuck open A vehicle that is running too hot can cause severe engine damage A good tune up should include testing the coolant for proper level The electric cooling fans on the radiator should also be checked for proper operation Other parts of the cooling system that should be checked include the radiator and heater hoses and water pump for leaks Unit 5 COMPUTER SYSTEMS In modern vehicles nearly all systems are electronically controlled Ignition systems emission controls fuel delivery controls and transmission controls are controlled by the PCM powertrain control module Some vehicles use several different control modules but they all communicate on a network Automotive networks have evolved over the years Most modern vehicles have several communication networks that perform several different jobs All vehicle
107. ven by the cam or crankshaft The oil pump draws its supply of engine oil through the pickup tube From the oil pump pressurized oil is usually first delivered to the oil filter and then to the main oil galleries for A distribution to other engine parts Se Page 31 of 67 MLR Engines eBook 2013 Melior Inc These main galleries feed the crankshaft bearings and then the connecting rod bearings via passages in the crankshaft Other branches of the main oil galleries feed oil to the camshaft and valvetrain components After the oil is pumped across the bearing surfaces of all moving parts it sprays oozes or drips away At various points inside the engine the oil then flows into drain holes that collect it and return it to the crankcase The oil pump must provide pressure at all engine operating speeds The faster the oil pump turns the more oil is pumped and so a pressure relief valve is used to divert excess pressure at high speeds Also a bypass valve near the oil filter opens in the event of a clogged filter to prevent oil starvation Correct bearing clearance is critical to maintaining oil pressure All engines lose a certain amount of oil pressure over time as normal wear increases bearing clearances As these clearances become excessive oil pressure bleeds off reducing the flow of pressurized oil to other parts of the engine This in turn can cause the valve train to become noisy and PURLTER wear rapidly Also when
108. verter whose primary purpose is to control exhaust emissions However a deterioration of the materials inside the converter possibly due to a prolonged misfire condition can cause an exhaust restriction that may have a significant effect on engine performance Page 63 of 67 MLR Engines eBook 2013 Melior Inc If an exhaust restriction occurs the complaint might be lack of power To determine if there is a restriction check exhaust system backpressure using service manual procedures CAUTION Don t forget that exhaust system components get very hot after the engine has been running Catalytic converters get especially hot and have been known to start dry grass fires Ensure proper ventilation to avoid asphyxiation when running an engine to check for exhaust leaks Emission Controls When the Industrial Revolution began in the 19th century the practices of industries and a growing population soon began to have a significant damaging effect on the environment Pollution of the air and water became a serious problem and eventually regulations were enacted to curb the releasing of harmful pollutants into the environment As the number of motor vehicles on the road steadily increased during the 20th century it became evident that vehicle emissions were a significant part of the problem that would have to be addressed California led the way by passing state laws to reduce vehicle emissions Its dense population centers and c
109. ween the piston and the cylinder wall Two types of rings are used compression rings which prevent combustion pressure from entering the crankcase and oil control rings which prevent engine oil from entering the combustion chamber above the piston Oil rings scrape excess oil from the cylinder walls for return to the crankcase Connecting Rods A rod connects each piston to the crankshaft The small upper end of the rod commonly has a bushing pressed into it A piston pin or wrist pin attaches the piston to the rod through this bushing which allows the rod to pivot as needed The larger lower end of the rod is attached to the crankshaft through rod bearing inserts that are stationary relative to the rod and allow the crankshaft to turn within the rod ona film of oil Page 3 of 67 MLR Engines eBook 2013 Melior Inc Crankshaft The crankshaft is a strong alloyed iron or steel shaft that converts the up and down motion of the pistons into a turning motion that can be transmitted to the drive train The crankshaft is supported by the block in several places along its length The crankshaft rides in main bearings which are inserts similar to the rod bearings at these supports Where the crankshaft is connected to the rods and where it is supported by the block are called journals The crank is finely machined and polished at these places The crankshaft is also drilled with a network of oil passages to deliver oil under pres
110. while the engine is running 18 Repeat these steps for each valve assembly 19 Reinstall the valve train components and valve cover s 20 Reinstall the spark plugs and wires 21 Reinstall the engine accessories and connect the negative battery cable 22 Connect the exhaust ventilation equipment Note Be sure to use approved exhaust ventilation equipment when operating a vehicle in an enclosed area 23 Start the engine and check operation 24 Shut off the engine Disconnect the exhaust ventilation equipment Note Again this is a generic overview of the valve seal replacement process Manufacturer s specific published service procedures should be followed for the vehicle that you re working on Cylinder Head Removal and Disassembly As with engine removal there are so many different vehicle designs engine and drivetrain configurations and other variables that it would be impossible to come up with a valid generic set of cylinder head removal instructions Some vehicles may require that the engine assembly be removed from the vehicle before cylinder head removal because of space limitations Notes e When removing or reinstalling a cylinder head follow manufacturer s specific published service procedures and instructions for the vehicle that you re working on e Also follow standard safety guidelines and procedures when using engine cranes and stands lifting equipment and safety stands e Manufacturer s specific serv
111. y among manufacturers or divisions Displacement Commonly called engine size the displacement of an engine is the volume of all the cylinders added together In the U S engine displacement was expressed in cubic inches for many years In modern vehicles displacement is usually given in liters L or cubic centimeters cc The diameter of the cylinder is called the bore If the bore and the length of the piston stroke are known the volume of a cylinder can be calculated The simplest formula for calculating the volume of a cylinder is Bore2 x Stroke x 0 7854 cylinder volume This result is multiplied by the number of cylinders to arrive at the displacement of the engine The value of 0 7854 is pi 4 Using the formula to determine the displacement of a six cylinder engine with a bore of 10cm and a stroke of 8cm we find 100 x 8 x 0 7854 x 6 3 769 92 Page 9 of 67 MLR Engines eBook 2013 Melior Inc This would be expressed as 3770cc or approximately 3 8L Number of Valves and Valve Train Type In an earlier section we saw the operation of an engine with a single overhead cam We noted that a dual overhead cam DOHC engine has a cam for the intake valves and one for the exhaust valves A V type DOHC engine has four camshafts two for each bank Dual overhead cams are frequently used on engines that have more than two valves per cylinder Four cylinder engines typically have eight 12 or 16 valves A six cyl
112. ypical Wear Areas This graphic illustrates some typical engine wear areas Valvetrain components can can leak fluids Pistons and piston rings can wear Improper Service Improper service can cause engine mechanical problems and increased wear as well For example cleaning gasket surfaces with surface conditioning disks is NOT recommended by vehicle manufacturers The use of such surface conditioning discs dislodges Aluminum Oxide from the disk and metal particles which can lead to premature engine bearing failure In some cases this failure occurs in as little as 1 000 miles 2 200 km after the repair has been made Improper bolt torque when reassembling engine components can distort bearing or sealing surfaces when fasteners are overtorqued Undertorqued fasteners can loosen and cause problems ranging from fluid leaks to major engine failure when an engine component comes apart while running To effectively diagnose the wide range of possible engine mechanical problems requires more study than can be provided in this introductory course however some basic diagnostic information and testing methods will be provided to help you get started Understanding some of the test methods included will also help in your understanding of how an engine works why it works and what happens when it doesn t work properly Page 11 of 67 MLR Engines eBook 2013 Melior Inc A logical step by step approach should be developed an

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