DIFFICULT TO START
- Check for contaminated fuel.
- Check fuel pressure.
- Check for faulty throttle position sensor.
- Check for faulty coolant temperature sensor.
- Check for loss of crank signal to ECM.
- Check EGR system.
- Check fuel pump relay and circuit.
- Check for faulty in-tank fuel pump check valve.
- Check ignition system.
- Check for faulty Idle Air Control (IAC) operation (if equipped).
- Check for faulty main (or ECM) relay.
SURGES
- Check ignition system.
- Check PCM and ignition grounds.
- Check for contaminated fuel.
- Check for restricted fuel filter.
- Check fuel pressure.
- Check for injector leakage.
- Check for intermittent EGR at idle.
- Check for incorrect charging system voltage.
- Check for faulty PCV operation.
- Check for faulty throttle position sensor.
- Check oxygen sensor for silicone contamination from fuel or improper RTV sealant.
- Check for faulty MAP sensor.
- Check for faulty coolant temperature sensor.
- Use scan tester to ensure vehicle speed sensor reading matches actual vehicle speed.
- Check for faulty A/C operation.
- Check for faulty park/neutral switch.
LACK OF POWER
- Check ignition system.
- Check for faulty ECM or ignition grounds.
- Check ignition timing.
- Check for contaminated fuel.
- Check fuel pressure.
- Check for restricted fuel filter.
- Check EGR system.
- Check for restricted air filter.
- Check for faulty throttle position sensor.
- Check for faulty MAP sensor.
- Check oxygen sensor for silicone contamination from fuel or improper RTV sealant.
- Check for faulty coolant temperature sensor.
- Use scan tester to ensure vehicle speed sensor reading matches actual vehicle speed.
- Check A/C system operation.
- Check charging system voltage.
- Check power steering operation.
- Check for faulty automatic transmission operation.
- Check valve timing.
- Check for improper or worn camshaft.
- Check engine compression.
- Check for restricted exhaust system.
SPARK KNOCK/DETONATION
- Check for engine running hot because of low coolant or other cooling system faults.
- Check for correct fuel octane rating.
- Check knock sensor (if equipped) and circuit.
- Check for correct PROM or EEPROM.
- Check spark plugs for correct heat range.
- Check ignition timing.
- Check for low fuel pressure.
- Check EGR system operation.
- Check automatic transmission for correct shift points.
- Check for carbon build-up in cylinders.
HESITATION, SAG OR STUMBLE
- Check fuel pressure.
- Check for contaminated fuel.
- Check for binding throttle position sensor.
- Check ignition timing.
- Check MAP sensor operation (if equipped).
- Ensure charging system voltage is correct.
- Ensure ignition system is properly grounded.
- Check for faulty spark plugs or wires.
- Check canister purge system.
- Check EGR system.
CUTS OUT OR MISSES
- Check ignition system.
- Check spark plugs.
- Check secondary ignition wires.
- Check for restricted fuel filter.
- Check for faulty injector(s).
- Check fuel pressure.
- Check for vacuum leaks.
- Check engine compression.
- Check valve timing.
- Check for damaged or worn push rods, rocker arms, valve springs and camshaft lobes.
- Check throttle position sensor and circuit.
POOR FUEL MILEAGE
- Check fuel pressure.
- Check ignition timing.
- Check spark plugs.
- Check for correct tire pressure, vehicle carrying heavy loads or poor driving habits.
- Check if A/C is on all the time.
- Check for restricted air filter.
- Check for restricted exhaust system.
- Check for proper speedometer calibration.
- Check EGR system.
- Check compression.
- Check for dragging brakes.
- Check gasoline quality.
- Check for cooling system running too hot or cold.
ROUGH OR UNSTABLE IDLE
- Check fuel pressure.
- Check ignition timing.
- Check for leaking fuel injector(s).
- Check for restricted air filter.
- Check throttle position sensor operation.
- Check for open EGR valve at idle.
- Check PCV valve operation.
- Check oxygen sensor for silicone contamination from fuel or improper RTV sealant.
- Check for fuel in fuel pressure regulator hose, indicating a faulty fuel pressure regulator.
- Check knock sensor operation (if equipped).
- Check for correct charging system voltage.
- Check canister purge system operation.
- Check Idle Air Control (IAC) system operation (if equipped).
- Check MAP sensor (if equipped) operation.
- Check for high A/C pressure due to overcharge or faulty pressure switch.
- Check power steering pressure switch and circuit operation.
- Ensure battery cables are clean and tight.
- Ensure engine compression is correct.
EXCESSIVE EXHAUST EMISSIONS OR ODORS
- Check fuel pressure.
- Check ignition timing.
- Check charcoal canister for fuel saturation.
- Check PCV system operation.
- Check for faulty spark plugs.
- Check for lead contamination of catalytic converter.
- Check for improperly installed fuel filler cap.
- Check EGR valve operation.
- Check cooling system operation.
BACKFIRE
- Check ignition timing.
- Check ignition coil output.
- Check for faulty spark plugs.
- Check EGR system.
- Check for crossfire between spark plugs.
- Check for correct valve timing.
DIESELING (RUN-ON)
- Check for leaking injectors.
- Check for vacuum leaks.
- Check for carbon build-up in cylinders.
- Check for poor fuel quality.
Intermittent Simulation
To reproduce the conditions creating an intermittent fault, use the following methods
- Lightly vibrate component.
- Heat component.
- Wiggle or bend wiring harness.
- Spray component with water.
- Remove/apply vacuum source.
Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.
INTERMITTENT MALFUNCTION INDICATOR LIGHT (MIL)
- Check for electrical system interference from faulty relay, ECM-driven solenoid or switch. Faulty components can cause sharp electrical surge when operated.
- Check for incorrect installation of electrical options (2-way radios, cellular phones, etc.). Ensure EST ignition wiring is routed away from spark plug wiring. Ensure distributor is properly grounded.
- Check for ignition secondary circuit shorted to ground. Check for shorted MIL circuit. Check for poor ECM grounds.