GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1998 🢒 Riviera 🢒 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 .
    • Refer to Visual/Physical Checks.
    • Search for bulletins.

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

Fuel System
    • Check for incorrect fuel pressure. Refer to Fuel System Pressure Test (VIN 1) .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Ignition System
    • Check for proper ignition voltage output using the following steps:
       - Clip the spark tester J 26792 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 one end of another spark plug wire to the other coil tower; connect the other end of the spark plug wire to ground.
       - Crank the engine while observing the spark tester; a crisp blue spark should be observed.
       - Repeat the above steps for each coil.
    • If adequate spark is not present at the coil(s), check for the following conditions:
       - Coil(s) - Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Secondary Resistance
5000 - 8000 ohms (5K - 8K ohms)

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

VIN 1 Spark Plug Wires Resistance
3280 - 4921 ohms per meter (1000 - 1500 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 malfunctioning.

       - Malfunctioning ignition control module.
       - Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.
    • Remove spark plugs and check for the following conditions:
       - Fouled plugs
       - Cracks
       - Wear
       - Incorrect gap
       - Burned or damaged electrodes
       - Incorrect heat range
    • 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:

    • Check compression.
    • Sticking or leaking valves.
    • Worn camshaft lobe(s).
    • Valve timing.
    • Bent push rods.
    • Worn rocker arms.
    • Broken valve springs.
    • Excessive oil in combustion chamber-Leaking valve seals.
    • Low cylinder compression.
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Engine Mechanical for diagnosis procedures.

Additional Checks
    • Check Intake and exhaust manifold(s) for casting flash. Refer to Engine Mechanical .
    • Check TCC operation. Refer to Torque Converter Clutch Evaluation and Diagnosis in Automatic Transaxle 4T65-E.
    • Check the exhaust system for a possible restriction.
       - 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 System Check and/or Exhaust System .