GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2001 🢒 Park Avenue 🢒 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 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:
       - Intermittent crankshaft position (CKP) 18X signal
       - Intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position (CMP) sensor
       - Intermittent 3X reference signal
       - Intermittent camshaft position signal
    • Check the mass air flow (MAF) sensor conditions. Ensure that the MAF sensor honeycomb is not damaged.

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 injector harness is connected to the correct injector/cylinder.

Ignition System
    • Check for proper ignition voltage output using the following steps:
       - Clip the J 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 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 a component, replace that component and its mate.

       - Coils--Cracks, carbon tracking/arcing, or a secondary resistance value outside the specified range.

Coil Resistance
5,000-8,000 ohms (5K-8K ohms)

       - Spark Plug wires--Signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
9840 ohms per meter (3,000 ohms per foot)

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

       - Defective module
       - Ignition system wiring--Loose ignition module feed or ground connection, or damaged system wiring.
    • Remove spark plugs and check for the following:
       - Fouled plugs
       - Cracks

   Important: If carbon tracking is detected on a component, replace that component and its mate.

       - Check the spark plugs for carbon tracking on the porcelain and pitting on the plug wire contact.
       - Improper gap
       - Burned or damaged electrodes
       - Improper heat range or reach
       - 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 the engine for the following conditions:
       - Check compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber-leaking valve seals
       - Low cylinder compression
    • Check for incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnosis procedures.

Additional Checks
    • Check Intake and exhaust manifolds for casting flash.
    • Check the torque converter clutch (TCC) operation. Refer to Flexplate/Torque Converter Vibration Test in Automatic Transaxle.
    • Check exhaust system for possible restriction. Check the following:
       - Inspect exhaust system for damaged or collapsed pipes.
       - Inspect mufflers for heat distress or possible internal failure.
       - For possible plugged three-way catalytic converter. Refer to Restricted Exhaust in Engine Exhaust.