GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Sunfire 🢒 Engine 🢒 Engine Electrical 🢒 Backfire

Backfire

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DEFINITION: The fuel ignites in the intake manifold, or the fuel ignites in the exhaust system, causing a loud popping noise.

Preliminary Checks
    • Refer to Symptoms - Engine Controls .
    • Search the service bulletins.

Fuel System
    • Check for low fuel pressure. Refer to Fuel System Diagnosis .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Ensure each fuel injector harness is connected to the correct injector/cylinder. Refer to Engine Controls Schematics .

Ignition System
    • Check for proper ignition voltage output with the J 36012-A Spark Plug Jumper Wires and J 26792 Spark Tester or equivalent.
    • Check the spark plugs for the following conditions:
       - Wet spark plugs
       - Fuel-fouled spark plugs
       - Cracked spark plugs
       - Worn spark plugs
       - Improper spark plug gap
       - Burned electrodes
       - Heavy deposits
    • If the spark plugs are fuel or oil-fouled, determine the cause of the fouling before you replace the spark plugs.
    • Check the ignition control module (ICM) for proper ground connection.
    • Check the ignition coils for cracks or carbon tracking.

Engine Mechanical

Check for the following conditions:

    • The compression
    • Sticking valves
    • Leaking valves
    • Worn camshaft lobes
    • Improper valve timing
    • Broken valve springs
    • Excessive oil in combustion chamber, caused by leaking valve seals
    • Low cylinder compression
    • Incorrect basic engine parts--Inspect the following:
       - The camshafts
       - The cylinder head
       - The pistons
       - The other components

Additional Checks
    • Check intake and exhaust manifolds for casting flash.
    • Check the exhaust system for possible restriction. Check for the following conditions:
       - Damaged or collapsed exhaust system pipes
       - Heat distressed or internally-failed mufflers
       - A plugged 3-way catalytic converter--Refer to Restricted Exhaust in Engine Exhaust.