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

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DEFINITION: Fuel ignites in the intake manifold, or in the exhaust system, making loud popping noise.

Preliminary Checks
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Refer to Visual/Physical Checks in Symptoms - Engine Controls .
    • Search for bulletins.

Sensor/System
    • Check for the following intermittent ignition system conditions:
       - Check for an intermittent crankshaft position (CKP) Sync or CKP 18X signal.
       - Check for an intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position (CMP) sensor.
       - Check for an intermittent 3X reference signal.
       - Check for an intermittent camshaft position signal.
    • Check the throttle body inlet screen for foreign objects or damage that can affect the mass air flow (MAF) sensor airflow sample.

Fuel System
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Ensure each injector harness connector is connected to the correct injector. Refer to Fuel Injector Electrical Harness Removal from Rail .

Ignition System
    • Check for proper ignition voltage output using the following procedure:
       - Clip theJ 26792 Spark Tester to engine ground.
       - Connect one end of a spark plug wire to the spark tester. Leave the other end of the spark plug wire connected to the coil being tested.
       - Connect another spark plug wire between the remaining coil tower on the coil being tested and ground.
       - Crank the engine while observing the spark tester. A spark should be observed.
       - Repeat the above steps for each coil.
    • If spark is not present at the coils, check for the following conditions:

   Important:: If carbon tracking is detected on any component, replace that component and the component's mate.

       - Check the coils for cracks, carbon tracking or arcing, or a resistance value outside the specified range.

Coil Secondary Resistance
5,000-8,000 ohms

       - Check the spark plug wires for signs of arcing or cross-firing, cracks, carbon tracking, plug boot damage, pinched wiring, incorrect routing, or a resistance value more than the specified value.

Spark Plug Wire Resistance
9840 ohms per meter (3000 ohms per foot)

   Important: Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition components will arc to ground when a secondary component is malfunctioning.

       - Check for a malfunctioning ignition control module (ICM).
       - Check the ignition system wiring for a loose ignition module feed or ground connection, or damaged system wiring.
    • Remove the spark plugs.
    • Inspect the spark plugs for the following conditions:
       - Fouling
       - Cracks

   Important:: If carbon tracking is detected on any component, replace that component and the component's mate.

       - Check the spark plugs for signs of carbon tracking on the porcelain or arcing at the plug wire contact.
       - Check the spark plugs for incorrect gap. Refer to Maintenance Items in Maintenance and Lubrication.
       - Check the spark plugs for damaged electrodes.
       - Check the spark plugs for incorrect heat range. Refer to Maintenance Items in Maintenance and Lubrication.
    • If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

Engine Mechanical
    • Check engine mechanical for the following:
       - Check the compression. Refer to Engine Compression Test in Engine Mechanical.
       - Check for sticking or leaking valves. Refer to Cylinder Leakage Test in Engine Mechanical.
       - Check for worn camshaft lobes.
       - Check for valve timing.
       - Check for bent push rods.
       - Check for worn rocker arms.
       - Check for broken valve springs.
       - Check for excess oil in combustion chamber-Inspect for leaking valve seals.
    • Refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical for diagnostic procedures.
    • Inspect for incorrect engine parts, such as the following basic components:
       - The camshaft
       - The cylinder heads
       - The pistons, etc.
    • Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional Checks
    • Check intake and exhaust manifolds for casting flash. Refer to Upper Intake Manifold Replacement and Lower Intake Manifold Replacement in Engine Mechanical.
    • Check torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis in Automatic Transaxle-4T65-E.
    • Check the exhaust system for a restriction.
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the mufflers for heat distress or internal failure.
       - Check for a plugged 3-way catalytic converter. Refer to Restricted Exhaust .