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Chapter 31 Fuel Injection System Diagnosis and Service Service Precautions • Relieve fuel pressure before disconnecting components • Never turn the ignition on with fuel system components disconnected • Use the proper test equipment • Turn off the ignition switch before connecting test equipment Service Precautions (cont’d) • Disconnect both battery cables before arc welding an computer-controlled vehicle • Never disconnect the battery while the engine is running • Avoid static electricity charges when handling electronic components • Isolate or disable high-voltage systems before testing or servicing the fuel system Basic EFI System Checks • FI problems usually result in no-start or poor driveability problems • Check MIL first • No MIL or no DTC does not mean the system is operating normally • Fuel trim should be observed regardless of if a DTC is set Fuel Trim • The fuel trim monitor looks at the sum of the STFT and LTFT • If the PCM detects an extreme change in fuel strategy, a DTC will set • A fuel system DTC does not mean the fuel system is at fault Fuel Trim (cont’d) • STFT adjustments are temporary and are not stored in PCM memory • LTFT adjustments are stored and influence base timing and injector pulse width Fuel Trim (cont’d) • STFT responds to O2S information • Once a certain engine temperature is reached, the PCM starts updating LTFT • This is based on engine speed and STFT • If STFT shifts 3% and stays there, the PCM adjusts LTFT to bring STFT close to 0% correction Fuel Trim (cont’d) • Since V-type motors have two sets of O2S, a pair of STFT and LTFT numbers will show on scan tool • Both can vary in correction from bank to bank • Other systems can cause fuel trim to be out of range: – Air induction, PCV, ECT, ignition, exhaust, and O or A/F sensors Oxygen Sensor Diagnosis • Signal should vary between and volt • Activity is best checked with a scope • Voltage should switch quickly, A and C Manifold Absolute Pressure (MAP) Sensors • Increased manifold pressure (lower vacuum) causes increased injector pulse width • Reason for increased manifold pressure open throttle, vacuum leak, restricted exhaust, does not matter • Vacuum leaks with MAP sensors decreases idle air control counts Throttle Body • Designed to allow a certain amount of air to pass at a particular amount of throttle opening • Deposits reduce air flow • Some throttle bodies have a special coating and should not be cleaned with chemicals Fuel System Checks • Check fuel delivery – Low pressure can cause a lean condition or nostart – High pressure can cause a rich condition • Check fuel pressure and how long pressure holds with the key off • Inspect regulator for leaks Injector Tests • At Rest Test – Determines causes of system not holding pressure • Power Test – Uses a voltmeter or Noid light to determine if the injector is receiving power and is being pulsed to ground • Resistance Test – Uses an ohmmeter to check condition of injector coils Injector Tests (cont’d) • Balance Test – Helps isolate a clogged or dirty injector • Sound Test – Uses a stethoscope to listen for clicking of injector • Flow Test – Checks injectors after removing them from the engine • Oscilloscope Tests Conventional Injector Waveform Injector Tests (cont’d) • For all injector types, there should be a clean, sudden drop in voltage when turned on • Check voltage spike levels • High coil resistance or a shorted coil will reduce inductive kick when turned off • Current ramping can be used to compare current flow and voltage Injector Cleaning • Never soak an injector in cleaning solvent • Never use a wire brush, pipe cleaner, toothpick, or other tool to clean opening • Injector cleaning runs a chemical through the injector to remove deposits Fuel Rail, Injector, and Regulator Service • When removing and reinstalling components, lightly lubricate O-rings with engine oil or transmission fluid • Cap injector openings in the intake to prevent the entry of dirt or debris • Cap all fuel rail and injector openings • Do not use compressed air to flush or clean the fuel rail or injectors Idle Speed Checks – Non ETC • Check linkage and vacuum lines • Many different inputs will affect IAC: – – – – Lower than normal TP signal Higher than normal TP signal Incorrect ECT signal Stuck closed A/C switch IAC System Tests • Check IAC counts with a scan tool: – If counts are low or zero, look for a vacuum leak – If counts are higher than normal, look for a dirty or restricted throttle body – Look for count change while performing a wiggle test – Counts should be steady Servicing the IAC Motor • Some vehicles allow for IAC control via a scan tool • If the IAC does not respond, further testing is required • Carbon deposits in IAC passage can cause erratic idle speeds and stalling Cold Start Injectors • Should be checked with other injectors • Clean when other injectors are cleaned • The injector can be checked with an ohmmeter ... detects an extreme change in fuel strategy, a DTC will set • A fuel system DTC does not mean the fuel system is at fault Fuel Trim (cont’d) • STFT adjustments are temporary and are not stored in PCM... coating and should not be cleaned with chemicals Fuel System Checks • Check fuel delivery – Low pressure can cause a lean condition or nostart – High pressure can cause a rich condition • Check fuel. .. does not mean the system is operating normally • Fuel trim should be observed regardless of if a DTC is set Fuel Trim • The fuel trim monitor looks at the sum of the STFT and LTFT • If the PCM