MEASUREMENT IN TROUBLE DIAGNOSIS
Contents
1. MEASUREMENT IN TROUBLE DIAGNOSIS Foreword The information in this Training Manual should not be interpreted as a basis for warranty or goodwill claims against Nissan Motor Co Australia Pty Ltd NMA unless so designated This Technical Training Manual is intended for use by NMA amp Nissan Dealership Technical Personnel It is not designed for the use by press or for customer distribution Before quoting any specifications be sure to check the relevant Service Manual and Technical Bulletins Right for alteration to data and specifications at any time is reserved Any such alterations will be advised by Nissan through Technical and Sales Bulletins 2008 Nissan Motor Company Australia Pty Ltd Inc Victoria Ref Technical Training Department NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS Measurement of Pressure for Trouble Diagnosis When diagnosing vehicle concerns various measurements of pressure are often taken There are two types of pressure that we commonly refer to e Gauge pressure ranging from atmospheric pressure upwards e Absolute pressure ranging from a complete vacuum upwards Zero Zero Absolute Gauge Pressure Pressure Negative Positive Pressure gt I lt Pressure gt Complete Atmospheric Vacuum Pressure o lt _ lt __ _ gt a 100 kPa 60kPa OkPa 350 kPa 1 200 kPa 3 100 kPa 180 000 kPa2. However the gauge does no allow any pressure to escape but it does show the full supply pressure 3 Short to Ground Here the 3 4 diagram shows there is no restriction load such as a globe filament the flow runs out the end of the pipe directly from positive back to negative Therefore YES there is the flow of current present but it cannot be seen by the pressure gauge voltmeter The path offered by the gauge voltmeter is too restrictive It s easier for it to fully escape from the end of the hose If this was really a flow of electrical current the fuse would blow amp shut down the flow all together 10 MAINS PRESSURE FROM TAP 12kPa 12V Digital Battery Multi MAINS PRESSURE FROM TAP 12kPa 12V Battery MAINS PRESSURE FROM TAP 12kPa 12V Battery Nissan Australia April 2008 Digital Multi Meter A No Ground Connection Digital Multi Short to Ground NISSAN Learning Academy Measurement in Trouble Diagnosis MEASUREMENT IN DIAGNOSIS Measurement of Voltage Since electricity can t be seen by the naked eye technicians need to rely on key electrical concepts to understand how electrical circuits function and assist in locating faults Two important concepts that are often misunderstood are e Electrical Pressure e Voltage Drop 1 Electrical Pressure For current to flow in any circuit a difference in electrical pressure must exist A Voltmeter is used to measure the differe
3. Manifold Fuel Compression Compression Common Rail Vacuum Pressure Pressure Pressure Diesel injection petrol petrol petrol Diesel pressure idle Note Not to scale Gauge Pressure This is relative to atmospheric pressure and is most commonly used in system diagnosis Absolute Pressure This is measured from a perfect vacuum through to positive pressures This is less commonly used except for example when measuring intake manifold vacuum Vacuum A pressure of 0 kPa G Gauge is equal to 100 kPa A Absolute However when referring to vacuum from atmospheric pressure the readings increase in kPa to 100 kPa at a perfect vacuum This is actually a negative pressure kPa but is usually just expressed as kPa of vacuum NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS Measurement of the Fuel Pressure Petrol Engines As part of an Engine no poor running diagnosis the Fuel Pressure is an important measurement to record in order to narrow down the cause of a fault Measuring Fuel Pressure will measure the pressure that the fuel is under prior to entering the injector Obviously the Fuel won t spray properly if the pressure is incorrect too low Also the amount of fuel entering the combustion chamber will be insufficient if the pressure is too low Fuel starvation lf the Fuel Pressure is too high then the engine will have a rich running exce
4. condition 17 High internal High internal Brake Pedal Switch resistance 0 1 OHM Rear Brake Globe LH Globe RH 5 8 OHM combined total resistance Brake Pedal Switch resistance 0 1 OHM ag A Rear Brake oe 200 LED Centre gt Light Globe LH Globe RH 200 OHM Resistance
5. is switched OFF fuel pressure is retained in the lines for the specified period Typically this should be no more than a 10 drop over 10 seconds lf pressure is dropping away excessively consideration needs to be given to the following items e Leakage in the reverse direction back to the tank e Leakage in the forward direction through leaking injectors or fuel pressure regulator on Return Systems only If this is the case the engine will be difficult to start amp black smoke will be emitted from the exhaust Typical SST requirements for Fuel Pressure Testing Adapter y Adapter KV 101118400 ay KV 10117600 AUS p i a Dmm Gauge and Adapter Fuel Line Removal 7211 and 7273 Tool 16441 6N210 NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS Measurement of Compression in the Cylinder Chamber As part of an Engine no poor running diagnosis the Cylinder Compression is an important measurement to record in order to narrow down the cause of a fault Correct engine compression is a critical factor in good engine operation good fuel consumption and providing clean emissions Actual compression pressures will vary depending on the type and condition of the engine Typical range of compression ennai CompressionkPa kPa Max variation Cranking Sd Minimum eeens j Petrol VQ40 FC e a Diesel Indirect Injection TD42 2 942 2 452 Diesel Direct Inje
6. NITOR SPEC MONITOR NO DTC o 1600 3200 4800 6400 A F ALPHA B1 Well above 100 indicates there is an excess of AIR in comparison to fuel is entering the combustion chamber amp is being burned Well below 100 indicates there is an excess of FUEL in comparison to air is entering the combustion chamber amp is being burned RICH LEAN NISSAN Learning Academy Measurement in Trouble Diagnosis MEASUREMENT IN DIAGNOSIS Basic Principles of Electrical Given that Electricity can t be seen it can be difficult to determine electrical system faults Therefore if Electricity was likened to water flow it may assist with understanding how to diagnose electrical faults 1 Normally Operating Circuit Here the water flows from the tap battery through a hose wiring A pressure gauge voltmeter has been tapped into the hose to measure the line pressure The spray nozzle light globe at the end of hose shows a working circuit Due to the restriction globe filament there is a certain amount of pressure build up in the line This is measured by the pressure gauge voltmeter Some of the pressure is seen by the gauge the remainder of the pressure escapes through the nozzle 2 No Ground Connection Here the 2 diagram shows a circuit which can be likened to having no ground connection blockage in hose Therefore the only choice the pressure has is to follow the path offered by the gauge voltmeter
7. This will create a voltage signal which indicates to the ECM that the amount of fuel that was sprayed out of the injector was a large amount therefore next cycle it will decrease the injection rate NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS Ideal Air Fuel Mix 14 7 1 The right amount of Air to Fuel will result in an ideal burn LEAN by Short Injection Duration Excess of Air to Fuel The injector is opened for a short period of time by the ECM Only a small amount of fuel enters the combustion chamber This results in a short burn time therefore some O2 content will be left over after the burning has stopped This left over content of O2 is m expelled amp then seen by the O2 sensor This signals to I the ECM that the mix was lean therefore will result in Si 02 an increased rate of injection more fuel for the next gt Sensor cycle SMALL INJECTION QUANTITY LEAN by Fuel Starvation Injection Duration OK Excess of Air to Fuel Due to low fuel pressure blocked filter blocked injectors etc this results in a short burn time due to the lack of fuel This again results in some O2 content being left over This left over content of O2 is expelled amp then seen by the O2 sensor This signals to the ECM that the mix was lean therefore will result in an abnormal increase in the rate of injection for the next cycle in order t
8. al Update Bulletin EM06 001 3 Remove Glow Plugs ensure dirt cannot enter engine and glow plugs are not knocked around 4 Insert correct compression gauge adaptor for the engine NOTE Engine can be permanently damaged if incorrect compression gauge adaptor is used 5 Crank engine and after gauge stabilises RECORD compression readings for each cylinder Diesel Engine SST s for checking Compression YD25 Engine Refer to the right for the different glow plug hole adapter ED19600610 tools required for measuring compression on diesel engines NOTE 140mm Take care not to use the wrong adapter Otherwise severe engine damage will result Petrol Engines Use any commercially available tools for checking D30 Engine ED19600620AUS compression on petrol engines DO NOT use in YD engine or severe damage will result TD Engines ED19600600 NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS Measurement of Oxygen Content after Combustion All modern petrol engines have Oxygen Sensors installed in the exhaust manifold These sensors generate a voltage signal amp sends this voltage back to the ECM A varying amount of Oxygen seen by the sensor will create a varying voltage signal The ECM sees this varying voltage amp then it MAKES AN ASSUMPTION ON HOW MUCH FUEL ENTERED THE COMBUSTION CHAMBER If the Oxygen Sensor O2S measures a HIGH level of Oxy
9. ction ZD30 2 942 2 452 Diesel Direct Injection YD25 3 100 2 500 Ta Ta Compression Test Procedure All engine types Engine MUST be at operating temperature Ensure battery condition will enable correct cranking speed monitor with CONSULT II Use jumper battery if necessary lf the compression is below specifications e Check valve clearances e Conduct wet test Small qty of oil added to Low cylinder e If compression increases suspect rings piston problem e If compression remains same suspect valves cylinder head e If two adjacent cylinders remain Low suspect head gasket problem Petrol Engines 1 Remove fuel pump fuse crank engine a few times to ensure engine wont start 2 Remove manifold collector if required ignition coils and spark plugs 3 Insert compression gauge 4 Switch ignition ON and depress accelerator pedal fully NOTE The Electronic Throttle if fitted will open with ignition switched ON 5 Crank engine and after gauge stabilises RECORD compression readings for each cylinder NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS Diesel Engines 1 Ensure engine is warmed thoroughly amp then switch engine OFF 2 Refer to section EM or EC of the Service Manual for correct pump or fuel system disabling procedure NOTE On YD25 engines remove injector connectors and carefully isolate with insulation tape Refer to service Manu
10. gen This will tell the ECM the A F Ratio was LEAN Therefore on the engines next cycle the ECM will add MORE Fuel If the Oxygen Sensor O2S measures a LOW level of Oxygen This will tell the ECM the A F Ratio was RICH Therefore on the engines next cycle the ECM will add LESS Fuel Small Amount of Fuel LEAN This condition will create a situation where the A F mix will have a short burn time There is not enough fuel to make a long burn time Since the small quantity of fuel has quickly burnt up the burning will stop amp there will be a certain amount of Oxygen remaining amongst the exhaust gases These gases are expelled out the exhaust valve the O2 Sensor samples these spent gases amp there it will see this remaining O2 content This will create a voltage signal which indicates to the ECM that the amount of fuel that was sprayed out of the injector was a small amount therefore next cycle it will increase the injection rate Large Amount of Fuel RICH This condition will create a situation where the A F mix will have a long burn time There is now more fuel to make a longer burn time Since the larger quantity of fuel makes a longer burn time nearly the entire O2 content will burn The spent gases left over in the combustion chamber will contain very little if any O2 content These gases are expelled out the exhaust valve the O2 Sensor samples these spent gases amp there it will see that there is hardly any remaining O2 content
11. in the tank is low the fuel pump output is weak a fuel line is blocked or the fuel filter is blocked e If fuel pressure is too HIGH either the pressure regulator is faulty or the return line is restricted Intake Manifold Fuel Pressure _ Damper 7 Pressure Regulator Fuel Pressure Fuel Filter Gauge Not all models Fuel Return Fuel Pump Filter and Sender Unit Not all models Fuel Tank NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS Fuel Pressure Test on Return less Systems Injector Rail 1 Install the Fuel Pressure gauge on the engine Refer With Injectors to Section EC Basic Service in the Service Manual 2 Switch Ignition ON Ensure Fuel Pump activates amp then stops after a few seconds Check for fuel leaks 3 Start engine and read fuel pressure Compare to specifications in the Service Manual Fuel Damper e Blocked filter or fuel pump pick up e Restricted fuel lines e Faulty pressure regulator Check the following items if fuel pressure is too LOW Note F uel Tank e DO NOT SQUEEZE OR CRIMP FUEL LINES e If fuel pressure is too HIGH replace the pressure regulator which is located in the fuel tank Fuel Pump presite Filter and Regulator Sender Unit Pre set non variable Fuel Return Residual Pressure Retention Both types of Fuel Systems Ensure that when the engine amp fuel pump
12. nce in electrical pressure at any two points in a circuit Remember that Voltage in an electrical circuit is likened to water pressure in a pipe Pressure Difference in a Circuit For example in the circuit below the Voltmeter is used to detect the electrical pressure at various points in the circuit The Voltmeter s Positive lead is detecting the difference in electrical pressure between the battery Negative terminal to four other circuit locations The electrical pressure difference between the e A Battery Positive terminal and Battery Negative terminal 12V e B Switch output terminal and Battery Negative terminal 11 9 Volts e C Bulb power side and Battery Negative terminal 11 9 volts e D Bulb ground side and Battery Negative terminal O Volts Ground 12V Battery Ground lt _ eg eg eee Notice that the full battery voltage or pressure drops to 0 Volts as the circuit approaches ground 11 NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS 1 Electrical Pressure Cont d Here is the same electrical circuit with a fault The wiring is frayed amp current has to now make it s way through the resistance which is caused by the frayed damaged wire So now the electrical pressure difference between the e A Battery Positive terminal and Battery Negative terminal 12V e B Switch output terminal and Ba
13. nt Unburnt O2 means LEAN As a result the ECM increases the injection rate to add more fuel to an engine that doesn t need anymore fuel INTAKE AIR LEAK AIR LEAKS V EXHAUST Lr ae i a Sensor EXHAUST MANIFOLD LEAK NO SPARK NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS RICH Normal Air Quantity with Excess Fuel lf there is an excess amount of fuel added leaking injectors or excessive injection duration etc not all of the fuel will burn because in this case the burning will stop due to all the oxygen being burnt up RAW FUEL WITHOUT OXYGEN WILL NOT BURN ON IT S OWN The excess fuel will be expelled out of the exhaust valve however the reason why the O2 sensor will indicate RICH is because it cannot sense any O2 in the expelled exhaust gases NOT because of the raw fuel left over AN OXYGEN SENSOR CAN ONLY SEE OXYGEN It cannot see raw fuel RUNNING RICH FLOODING Using Air Fuel Alpha in CONSULT Il to indicate measured Oxygen Content Display A F ALPHA in DATA MONITOR or DATA MONITOR SPEC CONSULT If the A F Alpha shows a reading close to 100 typically 95 105 then the engine is running close to or at It s originally programmed map l e The ECM see no problems with the content of left over O2 it s measuring in the exhaust gases The balance of Fuel Quantity to Air Quantity in the engine is normal DATA MO
14. o compensate for the lack of fuel condition NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS LEAN by Intake Air Leak un metered air Injection Duration OK Excess of Air to Fuel Due to an air leak on the intake leaking intake manifold gasket hole in air intake tube etc the MAFS sensor only measures a certain amount of air This signal is sent to the ECM therefore the ECM adds a specific amount of fuel which is relevant to the amount of air measured Air which is leaking through a hole or a leaky gasket is added to the combustion chamber with an insufficient amount of fuel Combustion takes place but there is left over O2 in the exhaust gases amp therefore is seen by the O2 sensor This signals the ECM to increase the injection rate above what it thinks is normal False LEAN Signal due to Exhaust Leak Injection Duration OK Air Fuel Ratio normal REMEMBER If the O2 sensor sees Oxygen it means LEAN Therefore if O2 leaks into an exhaust manifold due to a cracked exhaust manifold or a leaking exhaust manifold gasket the false O2 content will make the ECM increase the injection rate EVEN IF THE INJECTION RATE WAS PERFECT False LEAN Signal due to Spark Missfire Injection Duration OK Air Fuel Ratio normal REMEMBER NO spark means NO burn Even if TOO MUCH fuel entered the combustion chamber if it doesn t burn neither does the O2 conte
15. ors the application of the brakes for fuel control Using the same input it also monitors small changes in Voltage Drop in the brake lamp circuit to determine if all the brake lamps are working Essentially the brake lamp circuit contains two groups of resistances in series creating a Voltage Divider circuit with the Brake Signal input to the ECM Rear Brake Lights OK The 1 diagram to the above right shows a normal brake light circuit The current from the battery travels through the close brake pedal switch contacts switch contacts always have a slight resistance in them amp then it has a choice of travelling to the rear brake lights or to the ECM The ECM at this point sees the voltage pressure in the circuit So the ECM knows if the brakes are being applied or not However seeing as all the Brake light globes are OK the current will flow to ground as this circuit has far less resistance So the ECM is NOT going to see the full 12V Rear Brake Light Globes OPEN Circuit Blown globes In this case the rear brake light circuit has a much higher resistance The current can only travel to ground through the LED rear window brake light So the voltage pressure build up in the circuit is sensed by the ECM ECM reads a higher voltage So the ECM now realises that there are no brake lights amp it drives in failsafe mode until the fault is rectified NOTE A bad ground connection or corroded bulb connections can cause the same
16. output terminals 0 1 Volts e E Wire from switch output to bulb input 0 volts e C Bulb 5 9 Volts example only will always vary dependant on bulb type e D Ground circuit from bulb output to Ground 4 Volts e F Directly across the battery shows the full difference 12V OV A 0 1V B 5 9V C veS amp Switch Du to resistance blockage some voltage pressure can be measured at the DMM 5 A Fo ag 8 oo J Q 9 amp Battery lt lt me Loose Rusted or Painted k connections are equal to high resistance POOR GROUND CONTACTS ARE THE MOST COMMON CAUSE OF ELECTRICAL FAULTS THIS IS THE COMMON CAUSE OF DTC s SUCH CAN U1000 amp U1001 TO BE LOGGED 15 NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS Ground Connection Voltage Drop When tracking down an electrically related fault it is important to do a Voltage Drop test across ground connections This is very important in high current circuits like the starting and charging system but should not be neglected in lower current electronic systems The ground should be tested with the circuit operating under as much electrical load as possible e Connect the Positive Voltmeter lead to the ground terminal e Connect the Negative Voltmeter lead to the grounding bolt or another clean ground area e Operate the circuit under load including t
17. ssive fuel consumption issue Fuel system tests are e Pressure e Residual Pressure Retention Ensure there is sufficient fuel in the tank before conducting tests Fuel Pressure Release On all systems it is important to safely release residual fuel pressure before removing fuel hoses e Perform FUEL PRESSURE RELEASE with CONSULT II in Work Support Mode Ensure that engine stalls and will not restart e Without CONSULT II remove the fuel pump fuse run the engine until it stalls and ensure that it will not restart WARNING Great care must be taken to avoid fires when opening the fuel system Fuel Pressure Test on Return Systems 1 Install the Fuel Pressure gauge on the engine Refer to Section EC Basic Service in the Service Manual 2 Switch Ignition ON Ensure Fuel Pump activates amp then stops after a few seconds Check for fuel leaks 3 Start engine and read fuel pressure Compare to specifications in the Service Manual Check the following items if fuel pressure is too Low e Blocked filter or fuel pump pick up e Restricted fuel lines e Faulty pressure regulator Note e If fuel pressure is LOW carefully squeeze the return line resulting in blocking it amp watch a sharp amp rapid increase to approximately double the normal Fuel Pressure spec Only do this for a maximum of 3 seconds If the pressure increase does occur the fuel pressure regulator is faulty If not either the level of fuel
18. tch output to bulb input 0 volts e a e C Bulb 9 9 Volts example only will always vary dependant on bulb type D Ground circuit from bulb output to Ground 0 Volts F Directly across the battery shows the full difference 12V OV A 0 1 V B E C D 13 NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS 2 Voltage Drop Cont d Here is the same electrical circuit with a fault The wiring is frayed amp current has to now make it s way through the resistance which is caused by the frayed damaged wire So now the Voltage Drop across the e A Battery Positive lead to the Switch Input OV e B Switch input amp output terminals 0 1 Volts e E Wire from switch output to bulb input 4 volts e C Bulb 5 9 Volts example only will always vary dependant on bulb type e D Ground circuit from bulb output to Ground 0 Volts e F Directly across the battery shows the full difference 12V Connection with high resistance 14 NISSAN Learning Academy Measurement in Trouble Diagnosis MEASUREMENT IN DIAGNOSIS 2 Voltage Drop Cont d Here is the same electrical circuit with yet another fault In this case the wiring is OK but now there is a bad ground contact So now the Voltage Drop across the e A Battery Positive lead to the Switch Input OV e B Switch input amp
19. ttery Negative terminal 11 9 Volts e C Bulb power side and Battery Negative terminal 7 9 Volts e D Bulb ground side and Battery Negative terminal O Volts D ee eee Se Connection with high resistance EE ae 12V Battery Ground lt 12 NISSAN Learning Academy Measurement in Trouble Diagnosis MEASUREMENT IN DIAGNOSIS 2 Voltage Drop As electrical current flows through any circuit or device for work to be done there must be a Voltage Drop across that circuit Voltage must be dropped from supply voltage to zero at the ground point However there are instances when additional Voltage Drop may be inadvertently built into a circuit through loose or dirty connections particularly in the ground circuit Any additional Voltage Drop robs the circuit of energy reducing its effectiveness To do acontinuity or resistance test with an Ohmmeter does not confirm the high load performance of a circuit and a Voltage Drop test should be performed Voltage Drop in a Circuit For example in the circuit below the Voltmeter is used to detect the voltage drop across various components in the circuit The Voltmeter s leads are detecting the difference in electrical pressure between the two points they are connected to at any one time The Voltage Drop across the e A Battery Positive lead to the Switch Input OV Switch input amp output terminals 0 1 Volts Wire from swi
20. urning on accessories or cranking the engine e Measure Voltage Drop across the connection Remove bolt screw g Inspect mating surfaces Reinstall bolt screw P for tarnish dirt rust ete securely So ma pe Clean as required to il a assure good contact Repairing Grounds When repairing or confirming ground connections it is important to remove the bolt inspect and clean the mating surfaces and then torque the bolt securely Ground cleaning procedure Check for added on accessories and any modifications to the ground circuits Check for proper crimps and that all wires are securely fastened Voltage Drop Limits Wire negligible lt 0 001 Volts Ground connection Approx 0 1 Volts Switch contacts Approx 0 3 Volts 16 NISSAN Learning Academy Measurement in Trouble Diagnosis Nissan Australia April 2008 MEASUREMENT IN DIAGNOSIS N16 Hatch Brake Lamp Failsafe Strategy An interesting application of applying a change in Voltage Drop is found on the N16 Pulsar Ser II Hatch Models with Electric Throttle Control only These vehicles are built for the European market and have a Failsafe strategy if both brake lamp bulbs are not working If this occurs the ECM will enter a Failsafe Mode and the engine will operate with a significant reduction in performance further details are found on STB EC05 011 This situation will prompt the driver to have the vehicle checked Like most vehicles the ECM monit
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