Engine Backfires

If fuel ignites in intake manifold or exhaust system and makes a loud popping noise, check the following items:

• Ensure exhaust system is not leaking.
• Check base timing and ensure timing advance system is functional.
• Using Spark Tester (ST-125), check output of ignition coils.
• Check for intake manifold gasket leak and TBI gasket-to-manifold leak.
• Check for proper valve timing.
• Check engine for sticking or leaky valves.
• Check ECM and ignition system for faulty grounds.
• Check throttle body dashpot adjustment (if equipped).
• Check throttle position sensor.
• Check coolant temperature sensor.
• Check air valve, ISC solenoid and idle switch operation.
• Check intake air system and throttle body electrical connections.
• Ensure fuel system pressure is correct.
• Check A/C vacuum solenoid valve (if equipped).