GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Eighty Eight 🢒 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 .
    • Refer to Visual/Physical Checks in Symptoms .
    • Search for bulletins.

Sensor/System
    • Check for the following intermittent ignition system conditions:
       - Check for an intermittent 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 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 MAF sensor airflow sample.

Fuel System
    • Check the fuel pressure.
       - Refer to Fuel System Pressure Test (VIN K) .
       - Refer to Fuel System Pressure Test (VIN 1) .
    • 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 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 spark should be observed.
       - Repeat the above steps for each coil.
    • If spark is not present at the coil(s), check for the following conditions:

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

       - Check the coil(s) for cracks, carbon tracking/arcing, or a secondary resistance value outside the specified range.

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

       - Check the spark plug wires for 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 ohms - 1500 ohms per foot)

VIN K Spark Plug Wires Resistance
3280 - 4921 ohms per meter (1000 ohms - 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.

       - 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:
       - Check the spark plug(s) for fouling. Refer to Spark Plug Visual Diagnosis .
       - Check the spark plug for cracks.
       - Refer to Spark Plug Visual Diagnosis .

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

       - Check the spark plugs for signs of carbon tracking on the porcelain or arching at the plug wire contact. Refer to Spark Plug Visual Diagnosis .
       - Check the spark plugs for incorrect gap. Refer to Spark Plug Visual Diagnosis .
       - Check the spark plugs for burned or damaged electrodes. Refer to Spark Plug Visual Diagnosis .
       - Check the spark plugs for incorrect heat range. Refer to Spark Plug Visual Diagnosis .
    • If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Spark Plug Visual Diagnosis .

Engine Mechanical
    • Check engine mechanical for the following:
       - Check the compression.
       - Check for sticking or leaking valves.
       - Check for worn camshaft lobe(s).
       - Check for valve timing.
       - Check for bent push rods.
       - Check for worn rocker arms.
       - Check for broken valve springs.
       - Check for excessive oil in combustion chamber-Leaking valve seals.
       - Check for low cylinder compression.
    • Refer to Base Engine Misfire Diagnosis for diagnostic procedures.
    • For incorrect basic engine parts. Inspect the following. Refer to Engine Overhaul .
       - Check the camshaft.
       - Check the cylinder heads.
       - Check the pistons, etc.
    • Refer to Engine Overhaul for diagnosis procedures.

Additional Checks
    • Check intake and exhaust manifold(s) for casting flash. Refer to Intake Manifold Cleaning and Inspection .
    • Check TCC operation. Refer to Functional Test .
    • Check the exhaust system for a possible restriction.
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the mufflers for heat distress or possible internal failure.
       - Check for a possible plugged Three-Way catalytic converter. Refer to Restricted Exhaust System Check and/or Restricted Exhaust .