GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 Sonoma Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 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 Symptoms .
    • Search for service bulletins.

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

Ignition System
    • Test for proper ignition voltage output with a J 26792 Spark Tester or equivalent.
    • Inspect the spark plugs for the following conditions:
       - Wet or fuel fouled
       - Cracks
       - Wear
       - Improper gap
       - Burnt electrodes or heavy deposits
    • If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
    • Inspect the ignition control module (ICM) for proper ground connection.
    • Test the ignition coils for cracks or carbon tracking.
    • Test/inspect the spark plug wires for proper resistance and condition.

Engine Mechanical
    • Inspect engine mechanical for the following conditions:
       - Compression, refer to Engine Compression Test in Engine Mechanical
       - Sticking or leaking valves, refer to Valve Train Diagnosis in Engine Mechanical
       - Worn camshaft lobes, refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical
       - Valve timing, refer to Camshaft Timing Chain and Sprocket Cleaning and Inspection in Engine Mechanical
       - Bent push rods, refer to Valve Train Diagnosis in Engine Mechanical
       - Worn rocker arms, refer to Valve Train Diagnosis in Engine Mechanical
       - Broken valve springs, refer to Valve Train Diagnosis in Engine Mechanical
       - Excessive oil in combustion chamber -- Leaking valve seals, refer to Oil Consumption Diagnosis in Engine Mechanical
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Additional Checks
    • Inspect for intake and exhaust manifold passages for casting flash. Refer to Intake Manifold Cleaning and Inspection and Exhaust Manifold Cleaning and Inspection in Engine Mechanical.
    • Inspect the exhaust system for the following conditions:
       - 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 .