GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2002 🢒 LeSabre 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 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) sensor Sync or 18X signal.
       - Check for an intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position 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 airflow (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.

Ignition System
    • Check for the 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 J 26792 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 J 26792 spark tester. A spark should be observed.
       - Repeat the above steps for each coil.
    • If spark is not present at the plugs, check for the following conditions:

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

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

Coil Secondary Resistance
9840 ohms per meter (3000 ohms per foot).

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

Spark Plug Wires Resistance
1000-1500 ohms/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 malfunctioning.

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

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

       - Check the spark plugs for carbon tracking on the porcelain and pitting on the plug wire contact.
       - Check the spark plugs for fouling.
       - Check the spark plugs for cracks.
       - Check the spark plugs for incorrect gap.
       - Check the spark plugs for burned or damaged electrodes.
       - Check the spark plugs for incorrect heat range. Refer to Maintenance Items .
    • If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
    • Check for the following intermittent ignition system conditions:
       - Check for an intermittent crankshaft position (CKP) sensor Sync or 18X signal.
       - Check for an intermittent ignition feed circuit or sensor ground circuit to the CKP sensor or the camshaft position (CMP) sensor.
       - Check for a intermittent 3X reference signal.
       - Check for a intermittent CMP signal

Engine Mechanical
    • Check engine mechanical for the following conditions:
       - Compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Incorrect valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chambers or leaking valve seals
       - Low cylinder compression
    • Refer to the appropriate procedure in Engine Mechanical.
    • Refer to the appropriate misfire procedures in Engine Mechanical. Inspect the following components for correct engine parts:
       - The camshaft
       - The cylinder heads
       - The pistons, etc.

Additional Checks
    • Check the intake and exhaust manifolds for casting flash.
    • Check the torque converter clutch (TCC) operation. Refer to Diagnostic Starting Point - Automatic Transmission in Automatic Transaxle - 4T65-E
    • Check the exhaust system for a possible restriction:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the mufflers for heat distress or internal failure.
       - Check for a plugged three-way catalytic converter--Refer to Restricted Exhaust in Engine Exhaust.