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Chapter 46 - Goodheart

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1. A dynamometer often referred to as a dyno is used to measure an engine s power output and performance By loading the engine the dynamometer can check engine acceleration maximum power output and on the road performance characteristics Figure 46 13 shows a chassis dynamometer If you are having trouble finding a driveability problem you might perform diagnostic tests while oper ating the vehicle on a dynamometer This will let you simulate any condition that causes the problem For example you could connect a five gas exhaust analyzer to the tailpipe and operate the vehicle under load on the dynamometer Figure 46 14 You can also shift the vehicle through each gear accelerate to the speed at which the problem occurs walk around the vehicle to listen for abnormal noises or con nect listening devices all while simulating driving con ditions on the dyno Using an Oscilloscope An oscilloscope often called a scope is a piece of test equipment that displays voltages in relation to time When connected to circuit voltage the scope produces a line on a cathode ray tube or a liquid crystal screen The line illustrates the various voltages present in the circuit over short periods of time By comparing the scope pattern line shape to a known good pattern the technician can determine whether something is wrong in the circuit An oscilloscope is Rollers for car s drive wheels Figure 46 13 A chassis dynamometer will m
2. A certain amount of time is needed to properly ignite and burn the air fuel mixture Scope Sweep Rate Scope sweep rate is the frequency or time division shown on the screen during each test The sweep rate adjustment affects the horizontal or time measurement The scope sweep rate must be set to match the waveform frequency to be analyzed Sweep rate is commonly given in milliseconds ms A low scope sweep rate will compress the waveform and too much information will be shown at once A high sweep rate will expand the waveform and only a small section of the complete waveform will be displayed Trial and error adjustment of sweep rate is commonly used The sweep rate knob or sweep knob time division on the scope is turned until the desired wave form is displayed on the screen Compare the waveform pattern on the scope to a known good pattern Ignition System Patterns A vehicle s ignition system is designed to produce wide fluctuations in voltage When an ignition system is functioning properly these voltages will be within specifications A component with higher than normal resistance open spark plug wire for example would be indicated on the scope as a higher than normal voltage trace The high resistance would produce a high voltage drop A shorted component fouled spark plug would have low resistance and would produce a lower than normal voltage trace An oscilloscope s controls allow it to display either the p
3. verify c the type of sensor under test Figure 46 27 Throttle position sensor can also be checked with a scope A Probe through wires or use jumpers so power can be connected to sensor B Potentiometer or variable resistor TPS should produce smooth curve as throttle is moved open and closed Spikes indicate sensor problem C Switching type TPS should produce good square wave without ringing Fluke Probe to correct wire A Scope yr The upper horizontal lines should reach reference voltage Voltage transitions should be straight and vertical Peak to peak voltage should equal reference voltage Voltage drop to ground should not exceed 400mV If the voltage drop is greater then 400mV look for a bad ground at the sensor or ECU The lower horizontal lines should almost reach ground Signal frequency increases as throttle is opened vacuum decreases As the throttle closes the frequency decreases High engine load K Low engine load A high voltage level indicates high intake manifold pressure low vacuum As the throttle plate opens manifold pressure rises manifold vacuum lowers lt A low voltage level indicates low intake Cc manifold pressure high vacuum Figure 46 28 Manifold absolute pressure sensor can also be checked with scope A Here scope is probing through con nector to test MAP sensor Other lead is grounded B Signal frequency should increase with engine
4. 44 Emission Control System Testing Service and Repair ECM Scope Testing A scope can be used to check the output pulses leaving an electronic control module You can measure and observe the pulses going to fuel injectors solenoids and servo motors You can also check the reference voltage being sent to sensors Figure 46 32 Since ECM testing varies and is complex always refer to the service manual for detailed instructions You must compare your test waveform or voltage to known correct values If the ECM fails to produce a good pulse or reference voltage it should be replaced 7 Note For more information on ECM service refer to the index This subject is covered in several other chapters Flight Record Test A flight record test stores the sensor or actuator waveform in the scope s memory when a problem occurs For example when trying to check an intermittent problem connect the hand held scope to the sensor and test drive the vehicle When the problem occurs press the storage button on the scope The scope will then store a picture of the sensor output for analysis Figure 46 33 at Computer or ECM Probe to service manual recommended wire 2b SmeO1 MULTIMETER YLT AC AC 0C Figure 46 32 A A scope will also check reference voltage going to sensors and the control pulses from the ECM to the actuators Compare readings and waveforms to service manual specifications B Reference volt
5. Normal consistent signals from magnetic sensor B When the problem occurs the scope will store a picture of the sensor signals Note how each signal varies possibly from intermittent open sensor coil windings or loose mounting Fluke B Figure 46 34 This technician has test driven a vehicle with a hand held scan tool connected to a flight recorder tester At the shop the data collected can be fed into a computerized ana lyzer for further evaluation This is useful on difficult to find problems OTC Div of SPX Corp 878 Section 8 Engine Performance wires rich or lean fuel mixtures inoperative fuel injec tors and other problems even before removing and inspecting parts Modems Some analyzers can transmit data over telephone lines for comparison to information stored in a larger mainframe computer by using a modem A modem is an electronic device that allows computer data to be sent and received over telephone lines Data can be sent back and forth between modems This allows the technician to access information that can be used to troubleshoot difficult problems Most dealer ships have modem equipped computer analyzers The analyzer is plugged into the vehicle s data link connector and the information is sent by modem to the mainframe computer A mainframe computer is a very large computer that can store tremendous amounts of data It can also do mul tiple tasks or transfer information to several computer an
6. a load test set the scope on parade and idle the engine between 1000 and 1200 rpm While watching the firing lines on the scope quickly open the injection throttle valve or carburetor throttle plate and release it The firing voltage should increase but it must not exceed certain limits The highest firing line should not be more than 75 of actual coil output Typically voltage should not exceed 15 kV in a contact point ignition or 20 kV in an electronic ignition The upward movement of the firing lines during the load test should be the same If any of the firing lines are high or low a defect is present Cylinder Balance Test A cylinder balance test also called a power balance test measures the power output from each of the engine s cylinders As each cylinder is shorted the tachometer should indicate an rpm drop During a cylinder balance test all cylinders should have the same percentage of rpm drop within 5 If a shorted cylinder does not produce an adequate amount of rpm drop the cylinder is not firing properly Study Figure 46 42 Caution O Never short a cylinder in a vehicle with a catalytic converter for more than 15 seconds converter damage could result If the rpm drop in one or more cylinders is below normal a problem common to those cylinders is indi cated The cylinders could have low compression burned valve blown head gasket or worn piston rings a lean mixture vacuum leak faulty fuel injector
7. car The voltages you get may vary due to low battery charge or other reasons but they should be very close The following conditions must be met before testing e Engine at operating temperature Closed loop Engine idling for engine run column e Test terminal not grounded Scanner not installed Voltage Voltage Voltage Key Engine Circuit On Run Open a0 o N aoa o 4 0O ol N F N 12 lt o ol N o o o o a Phd o _ o 5 PIN 5 P N 14 D R N D Value shown or less than that value Sensor return 5V reference Vacuum sensor output PWM EGR solenoid Throttle kicker IGN 1 power Air switching solenoid Ground to engine t Wide open throttle var variable Voltage Voltage Voltage Key Engine Circuit On Run Open Baro sensor signal 4 75 decreases with altitude TPS sensor signal Coolant temp sensor signal Air control solenoid Diagnostic test term A C W O T cutout 5 7L Coolant temp sensor return Not used Oxygen sensor HI Dist ref pulse HI IGN module bypass ESC 5 0L Not used 4th gear switch if used Trans converter clutch solenoid Trouble code memory power Not used Not used Ground to engine P N Park or Neutral D R Drive or Reverse If less than 1V rotate drive wheel to verify Figure 46 8 The service manual will usually
8. connectors are sealed and do not allow easy probing You may need to install a test connector or jumper wires between the two halves of the connector to probe sensor voltages When reading the sensor waveform make sure the peak voltage levels are equal to each other If one is short or missing inspect the trigger wheel for a broken tooth Peak to peak voltage levels should be within specifica tions See Figure 46 26B As with any sensor reference voltages wiring and other criteria will vary If in doubt always refer to the service manual for the vehicle being tested to get accu rate electrical values Throttle Position Sensor Testing To scope test a throttle position sensor TPS con nect the test leads to the sensor output wire and to ground Voltage should still be fed to the sensor from the ECM Move the throttle open and closed The TPS wave form should show a smooth curve without any spikes See Figure 46 27 874 Section 8 Engine Performance Crankshaft sensor Wires from ECM Crank P trigger wheel A a Scope Test leads PEAK PEAK FREQUENCY OUTY CYCLE Y PULSE WICTH Y i 50ms DIU i GENERAL SENSORS shKeys Corr AND CONTINUITY RANGE OHM OPEN CLOSE MOVE B Figure 46 26 Scope testing crankshaft position sensors is similar to testing magnetic distributor sensors A Since crank shaft sensors generate their own voltage signal connect scope to terminals as specified B Note the resul
9. datastream values B capture a snap shot of operating parameters C measure exhaust emissions D switch actuators on and off Technician A says an oscilloscope s primary pattern represents the high voltage changes in an engine s ignition system Technician B says an oscilloscope s primary pattern represents the low voltage changes in an engine s ignition system Who is right A A only B Bonly C BothA and B D Neither A nor B An oscilloscope is connected to an automobile engine to check ignition system operation The scope s primary pattern indicates a malfunc tion in this section of the ignition system Technician A says this malfunction should show up in the scope s secondary pattern Technician B says this malfunction will not show up in the scope s secondary pattern Who is right A A only B B onb C Both A and B D Neither A nor B The spark line on an oscilloscope s secondary pattern is almost straight and about one fourth as high as the firing line Technician A says this indicates normal ignition system opera tion Technician B says this indicates an igni tion system malfunction Who is right A A only B B only C Both A and B D Neither A nor B Each of the following is an oscilloscope test pattern used by auto technicians except A raster B parade C secondary imposed D cylinder select Technician A says low circuit re
10. or computer malfunction or other problems Cranking Balance Test A cranking balance test is done to check the engine s mechanical condition It can be used to isolate a cylinder with low compression due to a burned valve worn piston rings or other problems The analyzer will show how much current is drawn by the starter motor as each cylinder goes through its compression stroke High current draw means high compression stroke pressure Low current draw low display line means that cylinder has low compression Look at Figure 46 43 882 Section 8 Engine Performance Right bank Left bank Cylinder power balance Push buttons ist 2nd 3rd 4th 5th 6th 7th 8th Cancel 1 8 4 3 6 5 7 2 Engine firing order Figure 46 42 A cylinder balance test is done by pressing but tons on analyzer control panel Each button will short and dis able one cylinder If the engine rom does not drop sufficiently that cylinder is not producing enough power Note how each button corresponds to the firing order A cylinder balance test will find any engine cylinder that is not producing power Some analyzers will short each cylinder automatically and keep a record of the results Other Analyzer Tests An analyzer is usually capable of performing other tests besides those discussed in this chapter These include starter cranking amps charging voltage and exhaust gas analysis Such tests are almost identical to those done with the individual instruments
11. results
12. s master automobile technicians The technician decides to begin his diagnosis by heating the ECM to normal operating temperature to determine whether it is causing the problem He starts the engine and lets it idle To ensure that he does not damage the ECM by overheating it he places the probe of a digital thermometer on the ECM case Next he uses a heat gun to warm the ECM When the ECM reaches 200 F the engine stalls The technician attempts to restart the vehicle without success Repair The technician installs a new ECU and takes the car for a test drive The vehicle operates properly Back at the shop the technician checks the ECM tem perature with the digital thermometer The ECM tem perature is 210 F and the car is functioning normally The test drive and diagnostic time are added to cus tomer s bill and the car is released to the owner Summary Strategy based diagnostics involves using a consistent logical procedure to narrow down possible problem sources A vacuum gauge measures negative air pressure produced by the engine fuel pump vacuum pump and other components A pressure gauge measures positive pressure pro duced by the engine turbocharger fuel pump or other device A diesel injection tester is a set of pressure gauges and valves for measuring system pressure A glow plug test harness can be used for checking a diesel engine rough idle problem Scan tool datastream values are live
13. 00 400 500 APM ENGINE 210 RPM CURRENT 170 AMPS BATTERY 10 2 VOLTS DIST RES 0 35 VOLTS DWELL 31 5 DEG 70 0 TIMING 0 0 DEG 610 PPM RESISTANCE 250 K OHMS ENGINE KILL 8 CYL TEMP 19 C TDC adh eee let eee 0 5 10 15 20 2500 RPM RPM 2385 1550 520 DWELL DEG 31 8 31 8 34 5 DWELL Yo 70 7 70 7 70 0 TIMING DEG 19 5 17 5 5 5 HC PPM 640 825 900 co o 3 85 4 25 4 0 AMPS A 22 3 32 4 35 0 VOLTAGE V 14 0 14 6 14 2 VACUUM HG TEMP 19 C Figure 46 36 Many modern analyzers are equipped with a dig ital display or extra screen A Digital display for cranking tests B Digital display for running tests Snap on Tool Corp Figure 46 37 A printer will type or print analyzer test results Chapter 46 Advanced Diagnostics Figure 46 38 Most late model analyzers will give detailed instructions for connecting the various leads to the vehicle and for doing each test This simplifies analyzer operation considerably Snap on Tool Corp Analyzer Connections Analyzer connections differ with each type and model Nevertheless most have the same general test connections Modern analyzers will give you directions for connecting the test leads to the vehicle Figure 46 38 If not test leads should be connected as described in the user s manual Special leads and hoses may be provided for measuring starting current charging voltage engine vacuum fuel pump pressure sensor signals and exhaust gas content These leads are generally
14. 85 to 85 to BARO ENG 1 97 4 65 103 kPa 103 kPa 98 4 69 TP Angle ENG 1 0 0 0 0 0 0 0 0 0 11 8 6 Engine Load ENG 1 0 1 to 5 1 to 5 13 Within Within Engine Speed ENG 1 80 RPM of 80 RPM of 1730 Desired Idle Desired Idle 160 100 5 1 ms 5 2 ms 67 Varies 114 Varies Varies more more Rich to Lean Status Bn 1 Sen 2 Lean Rich ENG 1 Rich to Lean Status Bn 1 Sen 3 Lean Rich ENG 1 Fuel Trim Cell Enei o 1 f e Disabled Fuel Trim Learn Enabled ENG 1 Disabled Disabled Enabled Enabled Shrt Term FT Bn 1 ENG 1 0 128 2 0 t0 2 0 3 0t03 0 6 0 to 6 0 Figure 46 7 Scan tool datastream values can be helpful when you have performance problems but no trouble codes Datastream values are electrical values detected by the ECM If values from a pinpoint test do not match datastream values suspect wiring or ECM problems controls It is one of the last tools used in diagnostics as plugging the test box into the wiring harness usually at it is time consuming Figure 46 9 the ECM connector The breakout box is connected in parallel with the Then a multimeter is used to touch specific termi ECM wiring harness An inline connector is provided for nals on the breakout box The measured circuit values Chapter 46 Advanced Diagnostics 863 ECM TERMINAL VOLTAGE 5 0L V I N H This ECM voltage chart is for use with a digital voltmeter to further aid in diagnosis These voltages were derived from a known good
15. After studying this chapter you will be able to Use advanced diagnostic techniques to trouble shoot difficult problems Use scan tool snapshot and datastream values to find problems not tripping trouble codes Use a breakout box to measure circuit values Explain the principles of an oscilloscope Summarize how to use waveforms to analyze the operation of sensors actuators ECU outputs and other electrical electronic devices Evaluate ignition system waveforms Summarize how to use an engine analyzer Earlier chapters explained how to diagnose problems using a scan tool a multimeter and various specialized testing devices If these basic troubleshooting tools fail to pinpoint the source of the problem you may need to use more complex diagnostic methods to find and fix the trouble This chapter summarizes advanced methods used to troubleshoot difficult to locate problems It also intro duces the operating principles of vehicle analyzers with emphasis on using the oscilloscope Advanced Diagnostics Strategy based diagnostics involves using a consis tent logical procedure to narrow down the possible problem sources Basically the procedure involves veri fying the complaint making preliminary checks reading service bulletins performing service manual recom mended checks repairing the problem and rechecking system operation See Figure 46 1 At one time or another every technician encounters a problem that
16. ace engine rapidly See if the torque reac tion of the engine unit causes electric breaks Temperature ECM Cool with an icing spray or similar device Warmed Heat with a hair drier WARNING Do not overheat the unit Wet WARNING Do not directly pour water on components Use a mist sprayer Electric loads Load switches Loaded Turn on headlamps air conditioning rear defogger etc Closed throttle posi ECM ON OFF switching tion switch condition Rotate throttle position sensor body Ignition spark position Timing light Spark power check Try to flash timing light for each cylinder using ignition coil adapter SST Figure 46 2 This diagnostic chart shows how different factors and parts can cause abnormal operating conditions The technician can perform the service procedures listed to simulate intermittent problems Nissan the problem symptoms and basic pressure testing methods to isolate hard to find problems A vacuum pressure gauge reads both negative and positive pressures It can be used to check all the previ ously mentioned systems To use a vacuum pressure gauge or a vacuum gauge to check the engine connect the gauge to a vacuum fit ting on the intake plenum or manifold Start the engine and note the reading on the gauge Compare the gauge readings to normal readings Figure 46 3 shows typical vacuum gauge readings and explains what they mean To help pinpoint problems that cannot be duplicat
17. ages should meet specifica tions and the waveforms should reflect smooth dc voltage Fluke Engine Analyzer Computer Analyzer An engine analyzer also called a vehicle analyzer or computer analyzer consists of a group of test instruments that includes a scope a tach dwell meter a VOM an exhaust gas analyzer and sometimes a scan tool These tools are mounted in a large roll around cabinet The operation of each instrument is often controlled by a computer that interfaces all the testing devices See Figure 46 34 When connected to the vehicle the analyzer will help you check the condition of the engine and its support sys tems An engine analyzer will help find problems when a scan tool does not show a trouble code or an out of parameter operating value For example if an engine misfire is being diag nosed the analyzer will help find which parts are defective It will pinpoint fouled spark plugs open plug Chapter 46 Advanced Diagnostics 877 PEAK PEAK FREQUENCY OUTY CYCLE Y PULSE WIDTH w 20ms DIv nes COMTINUIFY OHM OFEN CLOSE CURSOR 1 ar CURSOR 2 E OQ m 1 60 Y E 160 maa 47 2 4 404 P i Z1I7DIVISIONS BEFORE STOP Z ms DIY DISPLAY RECORDED SITGHALI terheys a CURSOR BACK w SEARCH G PRINT RRT Figure 46 33 The flight record is a feature on some small hand held scopes Connect to a suspect sensor using long test leads and place the scope on seat during test drive A
18. al for that vehicle Maximum peak levels should be equal to each other If one is shorter than the other look for a chipped or bent tooth on the trigger wheel Minimum peak levels should be equal to each other If one is shorter than the other look fora The waveform signature is created chipped or bent from the unique shape of the trigger tooth on the trigger wheel tooth passing the pickup coil wheel Figure 46 23 Typical waveform from a magnetic distributor pickup Fluke Lead grounded Distributor Probe into wire from sensor Hand held scope we The upper horizontal lines should reach reference voltage Voltage transitions should be straight and vertical _ Peak to peak voltages should equal reference voltage The lower horizontal lines B should almost reach ground Figure 46 24 A This scope is being used to check the signal from a Hall effect sensor B Hall effect sensor signal The fre quency of the signal should increase as engine speed increases Fluke Optical Sensor Testing An optical sensor can also be tested with an oscillo scope You can probe the output wires from the sensor and compare the waveform to specifications An optical pickup test measures the output generated by the photo diodes as they are energized by the LEDs It is also easily done with a hand held scope probing into the sensor s electrical connector Again refer to the ser vice manual to find the connector pin num
19. alse data Numerous computer malfunctions or false outputs could result See Figure 46 10 To isolate the source of electromagnetic interference try turning off or disabling circuits or devices If for Noise from defective alternator diode Alternator diode noise B Figure 46 10 A Electromagnetic interference can come from a variety of sources and can cause major problems This wave form is caused by a defective alternator diode B This is the injector pulse waveform from the same vehicle Note the hump pattern similar to the alternator pattern IATN example removing the drive belt from the alternator corrects the problem suspect problems inside the alter nator If the problem only occurs with the heated wind shield turned on check components within the heated windshield circuit You can use a small transistor radio to find induced voltage sources Turn the radio on and set it on the AM band but do not tune it to a station If the shop is equipped with fluorescent lights turn them off or test the vehicle outside away from power lines and any other sources of EMI Move the radio around the engine compartment and under the dash with the engine running If EMI noise static is present a popping or cracking noise will be produced by the transistor radio You can also use a car antenna cable and the car radio as a noise sniffer See Figure 46 11 To correct an EMI problem you must stop the source of the interfe
20. alyzers at the same time The auto or equipment manufacturer s mainframe computer may contain information about common prob lems Steps for finding problems specific voltages and other electrical values for each model may also be stored in the mainframe s memory Engine Analyzer Differences There are a number of different makes of analyzers on the market The controls and meter faces may be orga nized differently but the basic test equipment and opera tion of each are almost the same See Figure 46 35 Most analyzers will check aE 4A TF a Figure 46 35 An analyzer can perform different tests and measurements It is like having a multimeter tach dwell exhaust analyzer timing light and other testers connected at once for problem evaluation Battery charging and starting systems Ignition system Engine condition Fuel system Emission control systems Sensor and ECM signals Analyzer Test Equipment Typically an analyzer will contain several pieces of test equipment including e Oscilloscope high speed meter that uses a liquid crystal display or a television picture tube Voltmeter ammeter and ohmmeter meters used to measure electrical values Tachometer meter used to measure engine speed in rpms It is commonly used when adjusting fuel injection ignition timing and idle speed Dwell meter instrument that measures ignition module or contact point conduction time in degrees of distributor r
21. bers for the optical pickup s output wire Optical sensors are used in a few distributor designs and are never used in crankshaft sensors An optical sensor s waveform should have straight sides and adequate voltage output The upper horizontal line on the waveform should almost reach reference voltage The bottom horizontal line should almost reach ground or zero See Figure 46 25 Remember that optical sensors are susceptible to dirt An oil mist or a film of dirt can prevent light transfer from the LEDs to the photo diodes Again refer to the manu facturer s service literature for specific information Chapter 46 Advanced Diagnostics 873 The upper horizontal lines should reach reference voltage Voltage transitions should be straight and vertical Peak to peak voltages should equal reference variations in the trigger wheel window Figure 46 25 Typical waveform generated by an optical sensor If the shutter blade widths vary the pulse width will also vary Fluke Crankshaft Position Sensor Testing Figure 46 26A shows how to use a hand held scope to test a crankshaft position sensor You can use the needle probe on the scope lead to check for an output signal without disconnecting wires This scope will show both ac output and a trace for voltage signal variations Note that this testing method would also work on engine block mounted magnetic crankshaft position sensors Tech Tip Some electrical
22. connected in the same manner as those covered in other chapters Figure 46 39 shows how to connect an analyzer to conventional and unitized ignition coils An adapter may be needed to connect the analyzer to a distributorless ignition system Figure 46 40A You must install sec ondary jumper wires on some direct ignition systems so the inductive test leads can be clamped around them to read voltages Figure 46 40B Using an Analyzer To use an analyzer plug the electrical cord into a wall outlet Set the controls and connect the test leads to the vehicle If needed read the operating manual for the analyzer Caution Before starting the engine make sure all leads are away from hot or moving parts The ana lyzer leads are very expensive and can be easily damaged by contact with a hot exhaust mani fold or a spinning fan blade or pulley See Figure 46 41 880 Section 8 Engine Performance To distributor side of coil To ignition switch Black to ground terminal adapter 1 spark plug wire plug wire Tach adapter lead B Figure 46 39 Analyzer connections to distributor ignition sys tems A Connection to an ignition system in which the coil is separate from the distributor B Connection to a distributor with unitized coil Set the parking brake and start the engine Many ana lyzer manufacturers recommend increasing engine idle speed to around 1500 rpm during scope tests Ignition Coil Output Test A
23. d again after it warms Touch the pyrometer s probe to the sensor to get a reading of its operating temperature This will let you compare sensor temperature and resistance readings with manual specifications Finding Temperature Related Performance Problems When an engine performance problem occurs only at a specific temperature suspect electronic parts Electronic circuits especially ignition control modules can be affected by temperature extremes To check a component for problems affected by tem perature use a heat gun to warm the component or a can of freeze spray to cool the unit If the problem occurs with the temperature change the unit is at fault and should be replaced See Figure 46 12 Figure 46 12 When intermittent engine problems appear to be caused by heat cold or period of engine operation suspect electronic control circuits in ECMs A Freeze spray directed onto the ECM may cause or solve engine performance problem If it does replace the ECM B If engine stops running when air from the heat gun is directed onto the ECM you have found problem sources Do not overheat ECM however or you could damage it Section 8 Engine Performance Caution Do not apply too much heat to an electronic module Excessive heat can damage compo nents Only match the engine operating temper ature of about 200 F 93 C Use a digital thermometer to monitor the temperature when heating the unit Using a Dynamometer
24. d by an open spark plug wire a wide spark plug gap a burned distrib utor cap side terminal or a burned secondary connection in a distributorless ignition High resistance requires higher voltage output from the ignition coil A short firing line indicates low resistance in the ignition secondary which may be an indication of 3 a VEER EPER EERE EL Tr a oO A Superimposed display has all patterns on top of each other It checks that all patterns are uniform a Oo a eee LEN Oo B Parade display has cylinder patterns side by side in firing order It is useful for comparing firing voltages Number one cylinder is on left with its firing line on the right De Oo oO oO C Stacked or raster has all cylinders one above the other It is useful for comparing duration of events Number one is on bottom Others are in firing order Figure 46 19 Three common scope test patterns A Superimposed B Parade pattern C Stacked or raster pattern FMC 870 Section 8 Engine Performance leaking spark plug wire insulation oil fouled spark plugs carbon tracking on the distributor cap or coil pack or similar problems Not as much voltage would be needed Raster Pattern In a raster pattern or stacked pattern the voltage waveforms are placed one above the other as shown in Figure 46 19C The bottom waveform is the number one cylinder The other cylinders are arranged in firing order from t
25. d retard ignition timing when you tap on the engine Section 8 Engine Performance Tap lightly Ground 1s next to sensor Wire disconnected Scope Amplitude changes Frequency j lt change B Figure 46 30 Knock sensor signal can also be analyzed with scope A Connect scope lead to knock sensor and other lead to ground Tap on engine with small hammer or wrench to produce output signal B Knock sensor should produce normal fre quency and amplitude signal when engine is tapped on Fluke Alternator Diode Testing Most analyzers are capable of checking alternator diode condition The scope will display the alternator s voltage output If the alternator diodes are good the pat tern should be wavy but almost even This was detailed in Chapter 34 Charging System Diagnosis Testing and Repair Electronic Fuel Injector Testing Oscilloscopes can also be used to check injector operation in an electronic fuel injection system Refer to equipment and service manual instructions for details Figure 46 31 shows typical waveforms for good and defective fuel injectors Figure 46 31 These are waveforms for electronic injectors A Normal injector pattern B Stuck injector C Open injector D Partially shorted injector Snap on Tool Corp Oxygen Sensor Testing An oscilloscope can be used to check the signal pro duced by an oxygen sensor Oxygen sensor testing and service is covered in detail in Chapter
26. e to slowly drift back and forth Figure 46 3 Typical vacuum gauge readings and possible causes Sonco 860 Section 8 Engine Performance l Figure 46 5 Always keep vacuum diaphragms in mind as a potential source of trouble They can rupture leak air and not operate properly A vacuum pump can be used to check the condition of the vacuum diaphragm To chassis fuel system Pump volume measurement 2AN Note Do not connect both ports at once When taking a reading vacuum or pressure leave other port open to atmosphere restriction pump pressure Vacuum Pump Tests A hand vacuum pump is commonly used to check vacuum actuated devices and vacuum diaphragms Since vacuum diaphragms are made of rubber which can rup ture or leak they are a common source of performance problems To check a vacuum actuated device connect the vacuum pump to the fitting Pump the handle and see if the device will hold a vacuum If it leaks the diaphragm or the device should be replaced Figure 46 5 Diesel Engine Testers A diesel injection tester is a set of pressure gauges and valves used to measure injection system pressure This tester will check fuel pump pressure and volume injector operation out of engine lubrication system pressure and other functions If diesel injection pressures are not within specifications repairs or adjustments are needed Refer to Figure 46 6 Manifold for pressure gauges Measuri
27. e to test com puter system sensors With the engine cranking a magnetic sensor should commonly produce A 5 volts peak to peak B 0 5 volts peak to peak C 1 5 volts peak to peak D 15 volts peak to peak How do you scope test a Hall effect sensor Which of the following is commonly used as part of an analyzer A Tach dwell B Oscilloscope C Multimeter D All of the above What is a scope digital display Most analyzers recommend that engine idle speed be increased to about rpm during scope tests Which of the following tests measures the power output from each of the engine s cylin ders A Load test B Cylinder balance test C Ignition coil output test D EFI injector test ASE Type Questions Technician A says that strategy based diagnos tics involves using a logical procedure to narrow down possible problem sources Technician B says that advanced diagnostic techniques are used when conventional tests fail to pinpoint a problem Who is right A A only B B onb C Both A and B D Neither A nor B Technician A says computer terminal values can be measured with a low impedance meter Technician B says computer terminal values should be measured with a digital VOM Who is right A A only B B onb C Both A and B D Neither A nor B A scan tool has the capability to perform each of the following tasks except A display
28. easure engine power output under road conditions It will also load the engine while other tests are performed Sun Electric Corp Figure 46 14 A five gas analyzer is often used to check the content of engine exhaust gases This will give added informa tion for finding the source of a performance problem when oper ating a vehicle on a dynamometer OTC Div of SPX Corp usually a major component of an analyzer However it may be mounted by itself on a small roll around cart or it may be part of a hand held scan tool or multimeter See Figure 46 15 Reading the Scope Screen The scope screen can give instructions display volt ages as a trace or give other values as digital displays The oscilloscope s ability to draw a trace or pattern of circuit voltages for very short time spans makes it very useful for testing ignition and computer system perfor mance You should learn to recognize good scope pat terns Then you can easily detect scope patterns that indicate problems Figure 46 15 This hand held scan tool also functions as an oscilloscope It can display voltages in relation to time Note the scope pattern on the screen Voltage is shown on the scope screen along the ver tical up and down axis or scale Voltage values are given on the right and left borders of the screen See Figure 46 16 With the controls set on kV the numbers on the screen represent kilovolts One kV equals 1000 volts 5 kV equals 5000 v
29. ed in the shop technicians will often mount the vacuum pressure gauge in the passenger compartment and run a long hose to the vacuum fitting on the engine This allows the vehicle to be driven while checking for intermittent vacuum or pressure problems It also allows the techni cian to monitor engine and other system values under load See Figure 46 4 Normal engine reading Vacuum gauge should have reading of 18 22 inches of vacuum The needle should remain steady Choked muffler Vacuum will slowly drop to zero when engine speed is high Burned or leaky valves Burned valve will cause pointer to drop every time burned valve opens Intake manifold air leak If pointer is down 3 9 inches from normal at idle throttle valve is not closing or intake gaskets are leaking Chapter 46 Advanced Diagnostics 859 Figure 46 4 A pressure vacuum gauge with a long section of vacuum hose is needed for road testing The vacuum gauge will read turbocharger or supercharger boost pressures while vehicle is driven Weak valve springs Vacuum will be normal at Worn valve guides If pointer fluctuates excessively idle but pointer will fluctuate at idle but steadies at higher excessively at higher speeds valves may be worn speeds allowing air to upset fuel mixture Sticking valves A sticking valve will cause pointer to drop intermittently Carburetor or fuel injection problem A poor air fuel mixture at idle can cause needl
30. electrical values measured with the vehicle running or driving A breakout box allows you to pinpoint test elec trical values at specific pins on the ECM or in the computer system Electromagnetic interference results from induced voltage into wires and can cause a com puter to malfunction Scope voltage is shown on the scope screen along the vertical up and down axis or scale Scope time may be given on the scope screen on the horizontal scale in degrees milliseconds or duty cycle A primary pattern shows the low voltage or pri mary voltage changes in an ignition system The secondary scope pattern shows the actual high voltages needed to fire the spark plugs The term superimposed means that all the cylinder waveforms are placed one on top of the other The parade pattern also called the display pat tern lines up the waveform for each cylinder end to end across the screen A magnetic sensor scope test is done by mea suring the output voltage from the sensor with the engine cranking Most electrical connectors are sealed and do not allow easy probing You may need to install a test connector or jumper wires between the two halves of the connector to probe sensor voltages An oscilloscope can be used to check the output pulses leaving an ECM or ignition module Chapter 46 Advanced Diagnostics 883 A flight record test stores the sensor waveform in the scope memory when a problem occurs An engine analyze
31. explained in other chapters Dupp s Garage E Problem Mr Farnsworth brings his 1999 Sierra pickup truck into the shop with an elusive problem When asked to describe the problem he says that the engine runs fine but loses all power after about an hour of highway driving After the vehicle sits for about 20 minutes it starts and runs again Mr Farnsworth says he has taken his truck to four different shops and none have been able to fix the problem Diagnosis Duff checks for trouble codes and finds none He also checks for obvious problems but finds nothing Since the vehicle must be driven for an hour non mi o CRANKING AMPS BAR GRAPH ms an B AMPS RPR 205 CYL AMPS RANGE START CLEAR SELECT TEST Se CRANKING AMPS BAR GRAPH ae RPR 225 CYL AMPS 188 175 cyl RANCE START ANP_PROBE CLEAR SELECT TEST ZERO Figure 46 43 Cranking balance tests are used to check gen eral engine compression If any cylinder does not load the starter motor as much as the others it has low compression pressure and a possible leak A All bar graphs are at the same height so all cylinders have same compression B The number 5 cylinder has a low bar graph indicating less com pression pressure Snap on Tool Corp before engine stops running Duff suspects that engine heat may be related to the problem especially since the ECM is located in the engine compartment on this vehicle He passes the job along to one of the shop
32. he bottom up The raster pattern is normally used to check timing or dwell variations between cylinders Expanded Display Some oscilloscopes have a control that allows one cylinder waveform to be displayed above the parade pat tern This arrangement is called an expanded display or cylinder select If a problem is located in one trace that trace can be expanded enlarged and moved up on screen for closer inspection Reading Oscilloscope Patterns To read a scope pattern inspect the waveform for abnormal shapes high or low voltages incorrect dwell or time periods Since there are so many variations of electronic igni tion waveforms refer to the scope operating manual or GM HEI Remote Coil GM HEI Integral Coil Ford Dura Spark Ford SSI and Dura Spark II Ford EEC and Il Ford EEC Ill Chrysler ELB and ESC another reference Locate an illustration of a good scope pattern for the particular ignition system and compare it to the test pattern Figure 46 20 shows electronic ignition waveforms from several manufacturers They can be used as a guide when troubleshooting Figure 46 21 shows the true spark and the waste spark that occur when one ignition coil in a coil pack fires two spark plugs at once Figure 46 22 gives several faulty scope patterns True firing ee ee ee Wasted firing Figure 46 21 Note the differences between true firing actual spark and wasted firing waste spark when one coil fi
33. his feature is often used when a problem is hard to find or when intermittent troubles are present Most scan tools can be programmed to automatically take a snapshot of operating parameters whenever a diagnostic trouble code is set If desired the snapshot feature can be triggered manually allowing the use of the snapshot even when the vehicle does not generate a trouble code The manual capture feature requires you to monitor operating conditions and to press a button on the scan tool when the problem occurs For example if a car only acts up when driving at a specific highway speed drive the vehicle at the trouble causing speed and scan under these conditions When the symptom occurs engine misses press the appropriate scan tool button to capture the operating values while the problem is happening After returning to the shop look for any operating parameter that is almost out of specs The operating parameter may not be tripping a trouble code but it may be affecting vehicle operation Sometimes two or more electrical values can be almost out of specs By using the information provided by the snapshot feature you can often determine what is causing the problem You might have two sensors ready to fail a poor electrical connection in combination with a mechanical failure etc Chapter 46 Advanced Diagnostics 861 Scan Tool Datastream Values Scan tool datastream values are live electrical values measured with the vehicle
34. ing An oscilloscope can also be used to check the output signal of a distributor pickup coil It will not only mea sure voltage but it will also show the shape of the signal leaving the pickup coil Magnetic Sensor Testing A magnetic sensor test is done by measuring the output voltage from the sensor with the engine cranking With a magnetic sensor connect the scope primary leads to the pickup coil Set the selector to primary and the primary height control to 40V Adjust the pattern length to minimum With the engine cranking an ac alternating current signal about 1 5V peak to peak should be generated Figure 46 23 Hall Effect Sensor Testing A Hall effect sensor test is best done by checking the sensor s output waveform with an oscilloscope Without disconnecting the circuit reference voltage probe the output wire at the sensor connector The service manual will give pin numbers for probing See Figure 46 24A A Hall effect sensor waveform should switch rapidly have vertical sides and have the specified voltage output typically about 4 5 volts peak to peak The top of the square wave should reach reference voltage and the bottom should almost reach ground or zero Signal fre quency should change with engine cranking speed or engine rpm See Figure 46 24B Hall effect pickups can be found in distributors and some crankshaft position sensors Since specifications vary for Hall effect sensors refer to the service manu
35. ng lower spike indicates faulty insulation This is usually caused by a defective spark plug wire distributor cap rotor coil wire or coil tower a a oO a EL EEG AE Ta oO Long spark line Caused by a shorted spark plug or partially grounded plug wire Reversed coil polarity The pattern is upside down This problem is usually caused by someone accidentally connecting the primary leads to the coil backwards The ignition will still work but not as well w De Consistently high firing line in one or more cylinders Caused by a broken spark plug wire a wide spark plug gap or a vacuum leak nh w o o o oO Consistently low firing line in one or more cylinders Caused by fouled plug shorted wire low compression valve not closing or rich mixture a Tm w e Oo i Oo a Oe AL ua EL o oO Sloped spark line usually with hash Caused by fouled spark plug w o De So Run the engine at about 1000 rpm While watching firing lines on scope snap throttle fully open then quickly release it Highest firing line peaks should not be more than 75 of coil output Figure 46 22 Examples of bad scope patterns Study the shape of each trace and the problems that cause each waveform FMC 872 Section 8 Engine Performance Analyzing Square and Sine Wave Signals When analyzing a square wave there are seve
36. ng transfer pump pressure Diesel injection pump Engine oil pressure test Measuring crankcase pressure Checking for fuel return line Figure 46 6 Diesel injection system testers can perform several tests Note the various test connections Ford Warning The operating pressures in a diesel injection system are high enough to cause serious injury Even a small fitting leak can allow high pressure fuel to spray out and puncture your skin or eyes A glow plug test harness can be used to find the cause of a cold start or rough idle problem in a diesel engine The harness is connected to each glow plug one at a time Then the ohmmeter is used to check the resis tance of each glow plug After a period of engine opera tion the resistance of each glow plug is checked again Combustion will increase glow plug temperature affecting its resistance An unequal change in glow plug resistance temperature indicates that a cylinder is not firing Advanced Scan Tool Tests In addition to retrieving trouble codes modern scan tools can be used for advanced diagnostic procedures For example the scan tool can take a picture of oper ating parameters at the moment a problem occurs dis play live operating values as an engine is running and check actuators for proper operation Scan Tool Snapshot A scan tool snapshot is an instantaneous reading of the operating parameters that are present when a problem occurs T
37. olts etc If a line on the scope screen extends from zero to 7 kV the scope is reading 7000 volts If the scope is set to read 0 10 volts for checking the ECM and its sensors a line five divisions tall would indi cate 5 volts Similarly a waveform five divisions tall would be a reading of 5 volts peak to peak from the top of the positive trace to the bottom of the negative trace Voltage is the most commonly used value on a scope screen As voltage increases the trace line on the scope moves up As voltage drops the trace line moves down a proportionate amount Scope time is given on the horizontal scale of the scope screen in degrees milliseconds or duty cycle Different scales may be given on the bottom of the screen for four six or eight cylinder engines These scales are calibrated in degrees of distributor rotation Degrees may also be given as a percentage for quick ref erence to any number of cylinders The scope screen may also have a milliseconds scale for measuring actual time This makes it possible to measure how long each spark plug fires in milliseconds Md Orit iwi Ii j jji Oy iw Figure 46 16 Scales on an oscilloscope screen allow you to measure voltage and time accurately A O 25 000 volt scale B O0 50 000 volt scale C Scale for measuring time in milli seconds D Scale for measuring in degrees Sun Electric Corp Chapter 46 Advanced Diagnostics 867
38. ope Pattern The secondary scope pattern shows the high volt ages needed to fire the spark plugs Figure 46 18 illus trates the secondary pattern for one cylinder Secondary Firing Section The secondary pattern starts on the left with the firing section The firing section will pinpoint problems with the spark plugs the plug wires the distributor rotor and the distributor cap Figure 46 18 The firing line is the tall spike or line representing the amount of voltage needed to cause the electric arc to jump across the spark plug gap It is normally the peak voltage in the ignition system Figure 46 18 The spark line shows the voltage used to maintain the arc across the spark plug electrodes Figure 46 18 Once the spark is started less voltage is needed to main tain the arc The spark line should be almost straight clean and about one fourth as high as the firing line Secondary Intermediate Section The secondary pat tern s intermediate section or coil oscillations section shows voltage fluctuations after the spark plug stops firing Typically the voltage should swing up and down four times four waves at low engine speeds This sec tion of the pattern will indicate problems with the igni tion coil or coil pack See Figure 46 18 The voltage oscillations will disappear at the end of the intermediate section as the ignition amplifier begins to conduct or the breaker points close Secondary Dwell Section The secondary pat
39. otation It will detect point misadjustment and other problems Timing light strobe light for ignition timing adjustment Most analyzer timing lights have a degree meter for measuring distributor advance Vacuum gauge gauge used to measure vacuum when checking the operation of the engine opera tion and various vacuum operated devices Vacuum pump pump capable of producing a supply vacuum for operating and testing vacuum devices Cylinder power balance tester unit for electri cally shorting out one or more fuel injectors or spark plugs It will determine if a cylinder is firing properly and producing power Exhaust gas analyzer measures the chemical con tent and amount of pollution in the vehicle s exhaust Scan tool often incorporated into analyzers for retrieving trouble codes and circuit operating values Digital display displays operating values for various components in alpha numeric form Modern analyzers display readings of various test values engine rpm charging system voltage exhaust gas content etc See Figure 46 36 Printer prints information about ignition timing dwell engine speed emission levels and other values on paper If repairs are needed the technician can show the customer the improper readings on the printout If the vehicle is in good condition the printout can serve as a record if later repairs are needed See Figure 46 37 CRANKING PINPOINT TESTS HOLO l I 919 100 200 3
40. r also called a vehicle ana lyzer consists of a group of test instruments including an oscilloscope tach dwell VOM exhaust gas analyzer and sometimes a scan tool A modem allows a shop owned analyzer to com municate over telephone lines with a larger main frame computer An analyzer displays operating values for various components in number form An ignition coil output test measures the maximum available voltage produced by the ignition coil A load or acceleration test measures the firing voltage of the spark plugs when engine speed is rapidly increased Important Terms Strategy based diagnostics Vacuum gauge Pressure gauge Vacuum pressure gauge Hand vacuum pump Diesel injection tester Glow plug test harness Snap shot Scan tool datastream values Breakout box Electromagnetic interference EMI Digital pyrometer Dynamometer Oscilloscope Scope screen Trace Scope time Scope sweep rate Primary scope pattern Secondary scope pattern Firing section Firing line Spark line Intermediate section Coil oscillations section Dwell section Primary superimposed pattern Secondary superimposed pattern Parade pattern Display pattern Raster pattern Stacked pattern Expanded display Cylinder select Base line Rising edge Leading edge On time High time Trailing edge Falling edge Off time Low time Amplitude Peak to peak voltage Flight record test Engine anal
41. ral things you should check They include e The base line is the reference line or zero volts e The rising edge or leading edge is where the square wave goes from zero to high voltage The on time or high time is the part where the square wave stays at maximum voltage The trailing edge or falling edge is the drop in voltage back to zero The off time or low time is where the square wave stays on the baseline The amplitude or peak to peak voltage of a Square wave is determined by the horizontal dis tance from the baseline to the high time You can inspect these sections of the waveform to determine if there is a problem Some common problems that can affect a square wave include e Low or high resistance in the circuit or its components e Faulty electronic circuit e Circuit contaminated by moisture When analyzing sine waves check the following e Analog peak to peak voltage Is the waveform voltage strong from top to bottom Analog wave shape Is the trace normal for a known good component Analog wave frequency lIs the distance between waves normal Analog wave smoothness Is there unwanted hair or static on sine wave Computer System Scope Tests An oscilloscope can be used to help you find com puter system problems When the scan tool does not find anything and you still have performance problems you may need to check sensor and ECM signals with a scope Distributor Pickup Coil Scope Test
42. range and to raster Technician B sets the function controls to the highest kV range and to display Who is right A A onb B B onb C Both A and B D Neither A nor B 886 Section 8 Engine Performance 14 Technician A says that during a scope load test a defective ignition system component will always produce an abnormal scope pattern at idle speeds Technician B says that during a scope load test a defective ignition system component may not produce an abnormal pat tern at idle speeds Who is right A A only B B onb C Both A and B D Neither A nor B A cylinder balance test is being performed on an automotive engine equipped with a catalytic converter Technician A says that during this test each cylinder should be shorted for at least 45 seconds Technician B says that during this test each cylinder should not be shorted for more than 15 seconds Who is right A A onb B B onb C Both A and B D Neither A nor B Activities Chapter 46 1 2 Study the instruction manual for an analyzer and demonstrate how to hook it up for a test des ignated by your instructor With an oscilloscope hooked up and working point out the three sections of an ignition sec ondary scope pattern Interpret the trace patterns of a scope set up to test the ignition system Scope test several sensors Make a sketch of the waveform produced by each with a written explanation of your
43. rence replace leaking spark plug wire use suppressing condenser etc or shield the affected system s wiring from the interference reroute the sensor wire or wrap the wire with foil type tape for example Radiation noise Chapter 46 Advanced Diagnostics 865 Wire from harness to computer Sniffer or antenna cable to radio A Move antenna cable or small transistor radio around dash and engine B Figure 46 11 A Electromagnetic interference can be caused by ignition secondary voltage leaking diode in alternator and other sources of voltage spikes or magnetic field B A cheap transistor radio or an extra antenna cable connected to vehicle s radio will listen or sniff for source of interference Radiation can upset operation of computer sensor signals and car radio General Motors Using a Digital Pyrometer A digital pyrometer is an electronic device used to measure temperature Measuring temperature can help you verify scan tool readouts and find hard to locate problems It is handy for advanced diagnosis of various systems and components A digital pyrometer can be used to check e Engine operating temperature e Exhaust temperature e Coolant temperature e Sensor temperature e Ambient temperature e Air conditioning outlet temperature You can test a temperature sensor while it is still in the engine by checking pyrometer readings against sensor resistance when the engine is cold an
44. res two spark plugs at the same time True firing starts the air fuel mix ture burning while the waste firing does nothing since the cylinder is on its exhaust stroke Snap on Tool Corp as Chrysler EIS Hall Effect Le Chrysler ESC Hall Effect r Chrysler EIS Ford TFI Prestolite BID Figure 46 20 Study the differences in secondary waveforms from various auto manufacturers Snap on Tool Corp to So o e All firing lines fairly even but too high Look for problems common to all cylinders worn spark plug electrodes excessive rotor gap coil high tension wire broken or not seated fully late timing excessively lean air fuel mixture or air leaks in intake manifold Maximum available voltage during coil test should be within the manufacturer s specifications Disconnect plug wire to check maximum coil output w e N So o oO No spark line Caused by complete open in cable or connector So al oO Poor vertical alignment of point open spikes Caused by worn or defective distributor shaft bushings cam lobes or breaker plate ao oS ho oS o Uneven firing lines Can be caused by worn electrodes a cocked or worn distributor cap fuel mixture variations vacuum leaks or uneven compression nh ie o So Oo With plug wire removed for coil output test a short intermittent or missi
45. rimary low voltage pattern or the secondary high voltage pattern of the ignition system The scope pat terns are similar but important differences should be understood To introduce the basic sections of a scope pattern the primary and secondary patterns for one cylinder will be explained More complex patterns for specialized tests will be covered later in this chapter Primary Scope Pattern The primary scope pattern shows the low voltage or primary voltage changes in an ignition system A primary scope pattern is shown in Figure 46 17 The primary ignition pattern has three sections firing intermediate and dwell Note how the voltages change in each section of the pattern The ignition secondary circuit cannot work properly unless the primary circuit is in good condition A problem in the primary circuit will usually affect the secondary circuit For this reason the secondary circuit pattern is checked more often than the primary pattern 868 Section 8 Engine Performance Firing section Intermediate A i section Dwell section I T T Ignition control module allows Ignition control primary module stops current flow primary points close current flow I I I I N points open Secondary oscillations a Primary oscillations iipienpeepeniyii aa Figure 46 17 Typical primary waveform for an ignition system Study the various sections of the trace Secondary Sc
46. rmed to help find intermittent problems in one particular vehicle Vacuum and Pressure Gauge Tests A vacuum gauge measures negative air pressure pressure lower than atmospheric pressure produced by the engine fuel pump vacuum pump and other compo nents It is a valuable tool for determining engine condi tion and testing vacuum actuated devices A pressure gauge measures positive pressures pres sures higher than atmospheric pressure produced by the engine turbocharger fuel pump or other device It can be used to check for high exhaust system back pressure restricted converter or system abnormal fuel pressure incorrect turbocharger boost pressure and other prob lems You must use your knowledge of system operation a Variable factor Influential part Target condition Mixture ratio Pressure r lator Remove vacuum hose and apply vacuum Remove vacuum hose and apply pressure Ignition timing Crankshaft Rotate distributor clockwise position sengor Retarded Rotate distributor counterclockwise Mixture ratio feedback eal Disconnect oxygen sensor harness connector ntrol Perform on board diagnostic system On board Diagnostic Test Mode II at 2000 rpm Idle speed IAC valve AAC Turn idle adjusting screw counterclockwise Ga Turn idle adjusting screw clockwise Electrical connection Harness connec Poor electrical connec Tap or wiggle Electric continuity tors and wires tion or improper wiring R
47. running and in some cases being driven They almost eliminate the need for a breakout box or pinpoint measurements of electrical values You can read the scan tool screen to see weak values or values that are almost out of specs In most cases you can choose which datastream values you want the scan tool to display For example you may want to look only at the inputs to the ECM If you have a performance problem but no trouble codes have been set study the datastream values Values that are almost out of specifications may signal a problem area Datastream values give added information for finding troublesome problems Figure 46 7 gives a few datastream values that can be read by a scan tool Scan Tool Actuator Tests Most scan tools can switch computer controlled actuators on and off This allows the technician to verify the operation of these components For example a scan tool can be used to fire an ignition coil control the idle speed motor or disable a fuel injector The scan tool can also be used to perform a power balance test This test involves disabling a fuel injector or spark plug in a specific cylinder while monitoring the corresponding rpm drop Power balance tests are detailed later in this chapter Checking Computer Terminal Values Computer terminal values can be tested at the metal pins of the ECM A digital VOM can be used to read ter minal voltage and resistance values These readings can then be compared to kno
48. scope ignition coil output test measures the max imum available voltage produced by the ignition coil A spark plug requires only about 5 20 kV for operation However the ignition coil should have a higher reserve voltage Without this extra voltage the spark plugs could misfire under load or at high engine speeds when voltage requirements are greater Test adapter Cover plate shown removed Spark plug Coil B and upside down jumper wires harness Figure 46 40 This is operating manual illustration for connecting an analyzer to distributorless and integrated direct ignition systems A Separate inductive leads are needed for each wire on this distributorless ignition system B Note jumper spark plug wires between coil pack and spark plugs Snap on Tool Corp To perform the coil output test set the analyzer con trols and display to the highest kV range Run the engine at 1000 1500 rpm Using insulated pliers disconnect a spark plug wire Hold the end of the wire away from ground while watching the scope screen Figure 46 41 When connecting an analyzer to a vehicle keep all cables away from hot or moving parts Test cables are very expensive to replace Tech Tip With a coil pack you must test each coil s output voltage separately Just because one coil passed its tests does not mean the others will By using the coil pack firing order and the sec ondary pattern you can tell which coil
49. sec tions differ Instead of mechanical contact points an igni tion module operates the ignition coil The circuit design inside the module determines the shape of the dwell sec tion If you are not familiar with electronic ignition wave forms they can be easily misinterpreted Scope Test Patterns There are five scope test patterns commonly used by the technician when checking ignition system operation primary superimposed secondary superimposed parade display raster stacked and expanded display cylinder select As you will learn each of these patterns is capable of showing certain types of problems Primary Superimposed Pattern The primary superimposed pattern shows the low voltages in the primary system the ignition module or the condenser coil primary windings and points Superimposed means that the patterns for all the cylinders are placed on top of one another This makes the trace line thicker than the single cylinder pattern dis cussed earlier Sometimes an experienced technician will inspect the primary superimposed pattern before going to the more informative secondary pattern Secondary Superimposed Pattern The secondary superimposed pattern places all the cylinder waveforms on top of each other but it also shows the high voltages produced by the ignition coils It is one of the most commonly used scope patterns The superimposed secondary waveform allows you to quickly check the operating condi
50. seems impossible to fix He or she might replace a part that seems bad only to find the same annoying symptoms when the repair is complete The new part must be removed and further diagnosis This sample chapter is for review purposes only Copyright The Goodheart Willcox Co Inc All rights reserved Advanced Diagnostics Figure 46 1 This chart shows basic steps of strategy based diagnostics Study the chart carefully General Motors 857 858 Section 8 Engine Performance completed until the real culprit is found This is when advanced diagnostic techniques come in handy By learning a few advanced tricks of the trade using datastream values a breakout box an oscillo scope and an analyzer even the most difficult problems can be located and corrected with minimal frustration When diagnosing problems use your knowledge of system operation to determine which part could be mal functioning and causing the symptoms For example if an engine misses only when cold think of which parts affect cold engine operation You should think of the coolant temperature sensor the intake air temperature sensor and the cold start injector These components are monitored and or controlled by the ECM which enriches the air fuel mixture when the engine is cold Service manuals contain information to help facili tate troubleshooting The chart shown in Figure 46 2 summarizes the basic service procedures that can be perfo
51. should be tested With the spark plug wire removed a tall firing line should stand out from the others Look over to the scope scale on the side of the screen Read the voltage even with the top of the spike This value should equal the capacity of the ignition coil Caution A few electronic ignitions may be damaged by disconnecting spark plug wires while the engine is running Be sure to check manufacturer s directions With older electronic ignitions coil output voltage should range between 30 000 45 000 volts However some electronic ignition coils are able to produce up to 100 000 volts A Warning Even though ignition coil or coil pack current is too low to normally cause electrocution the high voltage could injure you or cause a poten tially deadly heart attack If the ignition coil voltage is below specifications do not condemn the coil until completing further tests Low coil output could be due to low primary supply voltage leaking secondary wires or similar problems Eliminate these as sources of the problem before replacing the ignition coil Chapter 46 Advanced Diagnostics 881 Load Test A load test or acceleration test measures the spark plug firing voltages when engine speed is rapidly increased When an engine is accelerated higher voltage is needed to fire the spark plugs While a defective com ponent may produce a normal scope pattern at idle it may not operate properly under load To perform
52. sistance can affect a square waveform Technician B says high circuit resistance can affect a square waveform Who is right A A only B Bonly C BothA and B D Neither A nor B Chapter 46 Advanced Diagnostics 885 Technician A says an oscilloscope is one type of test equipment normally used in an engine analyzer Technician B says a timing light is one type of test equipment normally used in an engine analyzer Who is right A A only B B only C Both A and B D Neither A nor B A vehicle is brought into the shop with fuel injector problems Technician A says an engine analyzer can be used to detect certain fuel injector malfunctions Technician B says an engine analyzer is not capable of testing fuel injector operation Who is right A A onb B B onb C Both A and B D Neither A nor B An engine analyzer normally contains each of the following test instruments except A multimeter B dwell meter C test light D vacuum gauge An oscilloscope is being used to test an auto mobile s ignition system Technician A increases engine idle speed to about 950 rpm during this test Technician B increases engine idle speed to about 1500 rpm during this test Who is right A A only B B only C Both A and B D Neither A nor B An ignition coil output test is being performed on an automobile Technician A sets the func tion controls to the lowest kV
53. specify the electrical values that should be present at each terminal of the computer connector General Motors Section 8 Engine Performance Figure 46 9 A breakout box is usually the last tool used to find performance problems It is connected to the wiring harness in computer system Then a multimeter can be used to check ter minals on the breakout box for actual operating voltages resis tance and current values They can be compared to known good values or to datastream values to find the cause of the problem OTC Div of SPX Corp are compared to the manufacturer s specifications If the measured values are not within specifications you usu ally have a defective component or a wiring problem For example if a reference voltage out of the ECM is low the ECM is bad or the wiring between the ECM and the breakout box is faulty Isolating Electromagnetic Interference Electromagnetic interference EMI or radiation interference occurs when an induced voltage enters another system s wiring Sources of EMI can include loose misrouted or unshielded spark plug wires police and CB radios and aftermarket accessories In the past electromagnetic interference was limited to noise in the radio speakers In late model vehicles EMI can cause a computer controlled system to malfunction For example induced voltage from a loose spark plug wire could enter a sensor wire This unwanted voltage would then enter the computer as f
54. speed with digital MAP C Amplitude should increase with engine speed with analog MAP Fluke Chapter 46 Advanced Diagnostics 875 Airflow Ground sensor i Zo Test Harness jumpers to ECU Scope Wide open throttle maximum acceleration Idle air bypass compensating Airflow into the intake airflow into intake manifold manifold is increasing Damping action caused by air flap movement The upper horizontal lines should reach reference voltage m m i E ae Peak to peak voltages should equal reference voltage eee ae The lower horizontal lines Cc should almost reach ground Figure 46 29 Note basic method for testing analog and digital airflow sensors A Jumpers are being used to allow power to remain connected to sensor Probe service manual recom mended pins or wires B As flow increases analog airflow meter should produce more voltage C With digital airflow meter signal frequency usually increases with engine speed and airflow Fluke Knock Sensor Testing To test a knock sensor with a scope connect the scope test leads to the sensor Then tap on the engine next to the sensor with a small hammer or a wrench See Figure 46 30A This should make the sensor produce a signal that is similar to the one shown in Figure 46 30B Another way to check a knock sensor and the ECM is to measure ignition timing while tapping on the engine next to the sensor The ECM shoul
55. tern s dwell section starts when the ignition module conducts primary Firing section i Intermediate l i i I Laia Section gt Dwell section _ Ignition control module stops current flow Ignition control module allows Intermediate current oscillations flow Firing line Spark line pin Figure 46 18 A secondary waveform for one cylinder The firing line is voltage needed to fire the spark plug The spark line is voltage needed to maintain the spark across the plug gap Intermediate oscillations show the coil and condenser action Dwell is the amount of time primary current flows through the ignition coil current through the ignition coil In a contact point system it is the time when the points are closed The ignition coil is building up a magnetic field during the dwell section The dwell section will indicate problems such as a faulty ignition module burned contact points or a leaking condenser Contact point dwell related to point gap can be read by measuring the length of the dwell section along the bottom scale of the scope screen Tech Tip An electronic ignition can have different dwell periods from cylinder to cylinder However if the dwell varies in a contact point ignition it indicates distributor wear or damage The scope pattern for an electronic ignition will vary from the pattern of a contact point ignition The firing and intermediate sections are similar but the dwell
56. ting display Compare the waveform to the service manual description Manifold Absolute Pressure Sensor Testing A scope can also be used to test the operation of both analog and digital manifold absolute pressure sensors Accelerate the engine and note the changes in airflow signals going to the ECM Compare the amplitude and shape of the waveform to known good patterns This is shown in Figure 46 28 Mass Airflow Sensor Testing To test analog or digital mass airflow sensors using a scope probe the connector as recommended in the service manual Compare your scope readings to factory specifications and known good readings See Figure 46 29 Throttle Probe to position correct sensor TPS terminal A Scope z Defective TPS pattern Spikes in a downward direction indicate a short to ground or an intermittent Bear VONA open in the resistive carbon strips indicates wide open Voltage decrease throttle WOT identifies enleanment throttle plate closing Voltage increase identifies Minimum voltage enrichment indicates closed throttle plate DC offset indicates voltage at key on throttle closed Throttle at position other than closed Not necessarily wide open throttle Reference inging may indicate voltage worn contacts or loose throttle return springs Transitions should be straight and vertical Throttle Throttle opening and plate closed voltage transitioning To ensure proper results from your test
57. tion of all cylinders Look at Figure 46 19A For example if one spark plug is not firing properly the waveform for that cylinder spark plug will not align with the others The abnormal trace will stand out because the firing voltage is higher or lower than normal The secondary superimposed pattern is used to check for general problems in the ignition system If one of the waveforms is out of place the other scope patterns may be used to find exactly which component is causing the problem Parade Pattern The parade pattern also called the display pattern lines up the waveform for each cylinder side by side across the screen The number one cylinder is on the left The other cylinders are displayed in firing order going to the right Figure 46 19B The parade pattern takes the superimposed wave forms and separates each along a horizontal axis This makes the parade pattern useful for comparing firing voltages of each spark plug If one or more firing lines are too tall or short a problem is present in those cylinders During normal operating condition secondary volt ages will vary from 5 12 kV for contact point ignitions and from 7 25 kV for electronic ignitions The electronic ignition normally produces higher voltages because of the wider spark plug gaps needed to ignite lean fuel mixtures Chapter 46 Advanced Diagnostics 869 A tall firing line on the parade pattern indicates high resistance in the ignition secondary cause
58. wn good values Often the read ings are taken with one or more wiring harnesses con nected to the ECM This eliminates the need to unplug connectors when making electrical measurements Figure 46 8 shows ECM terminal voltages for a spe cific vehicle Note how the pin numbers correspond to certain circuits and electrical values Caution O Never connect a low impedance resistance analog meter or test light to a computer system unless instructed to do so by the service manual A low impedance meter or tester could draw enough current to damage delicate electronic devices Using a Breakout Box A breakout box allows you to check electrical values at specific pins on an ECM or in the system the ECM 862 Section 8 Engine Performance DATASTREAM VALUES For Cold Key On Cold Idle and Hot Idle Vehicle in PARK A C turned OFF no power steering load all ACC s OFF Brake Pedal Released For 55 MPH Cruise Vehicle in Drive 4 A C turned ON and no power steering load compare data after driving for approximately 1 mile Display Cold Key Scan Tool Parameter Data List Cold Idle Hot Idle Units ON Within Within Engine Speed ENG 1 80 RPM of 80 RPM of 1730 Desired Idle Desired Idle Desired Idle RPM ENG 0 700to 1200 550 to 675 720 ENG 1 9810110 5 01060 201028 TP Sensor vie ENG 1 0 63 1 7 pomy BO mY 1 06 11 0 0 8 0 8 20 C to 90 C to 90 C to 30 to 50 kPa 30 to 50 kPa MAP kPa V ENG 1 97 4 63 64 2 88
59. yzer Vehicle analyzer Modem Mainframe computer Ignition coil output test Load test Acceleration test Cylinder balance test Power balance test Cranking balance test 884 Section 8 Engine Performance Review Questions Chapter 46 Please do not write in this text Place your answers on a separate sheet of paper L 2 3 On the scope screen Define strategy based diagnostics A vacuum gauge measures __ air pressure A scan tool_____ is arrecord of the oper ating parameters present at the moment a problem occurs Electromagnetic interference can be caused by A loose wires B unshielded secondary wires C aftermarket accessories D All of the above A n is one of the last tools used when diagnosing computer system problems is given on the ver tical scale and is given on the horizontal scale One kV equals A 00 volts B 1000 volts C 10 000 volts D None of the above If a scope waveform is higher or taller than normal this indicates a higher than normal The scope pattern shows the actual volt ages needed to fire the spark plugs Sketch and explain the three major parts of a scope secondary waveform How do you read a scope pattern Electronic ignition system waveforms will vary depending on the make and model of vehicle True or False When analyzing a square wave what six things should be checked Summarize how you use a scop

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