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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2003 🢒 Century 🢒 Engine 🢒 Engine Electrical 🢒 Backfire

Inspection/Test

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

Preliminary
    • Refer to Intermittent Conditions before starting.
    • Search for bulletins.

Sensor/System
    • Inspect for the following intermittent ignition system conditions:
       - Monitor the 24X sensor and the CMP sensor signal present parameters on the scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Test all CKP sensor A and CMP sensor circuits for intermittents. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
       - Monitor the 3X parameter on the scan tool. If the 3X is not responding, inspect the CKP sensor B and circuits for intermittents. Inspect the ignition control (IC) circuit, IC timing control circuit, low resolution engine speed signal circuit and the low reference circuit for intermittents. If these circuits become open, or shorted may not set a DTC immediately, but are capable of causing driveability complaints. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • Inspect the mass air flow (MAF) sensor conditions. Ensure that the MAF sensor honeycomb is not damaged.

Fuel System
    • Test for low fuel pressure. Refer to Fuel System Diagnosis .
    • Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Ensure that each injector harness is connected to the correct injector/cylinder.

Ignition System
    • Inspect for proper ignition voltage output using the following steps:
        1. Attach the J 26792 Spark Tester to engine ground.
        2. Connect the spark plug end of the spark plug wire to the J 26792 . Connect the other end of the spark plug wire to the coil being tested.
        3. Connect the spark plug end of the companion spark plug wire to ground.

The companion spark plug wire is the wire attached to the corresponding coil tower.

        4. Crank the engine while observing the J 26792 . A spark should be observed.
        5. Repeat the above steps for each coil.
    • If spark is not present at the coils, inspect for the following conditions:
       - Coils--Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Resistance
5,000-8,000 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
3,000 ohms per foot (9,842 ohms per meter).

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

       - Defective ignition module
       - Ignition system wiring--Loose ignition module feed or ground connection, or damaged system wiring.
    • Remove spark plugs and inspect for the following conditions:
       - Fouled plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned or damaged electrodes
       - Improper heat range or reach
    • 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 Inspection .

Engine Mechanical

Inspect engine mechanical for the following conditions:

    • Test the compression--Refer to Engine Compression Test in Engine Mechanical.
    • 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
    • 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
    • Inspect intake and exhaust manifolds for casting flash.
    • Test the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis in Automatic Transaxle.
    • Inspect the exhaust system for possible restriction:
       - Refer to Restricted Exhaust in Engine Exhaust.
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the mufflers for heat distress or possible internal failure.
       - Test for possible catalytic converter restrictions by testing the exhaust system back pressure.