GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Sonoma Pickup - 2WD 🢒 Engine 🢒 Engine Electrical 🢒 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 - Engine Controls .
    • Search for service bulletins.
    • Connect a scan tool and look at the misfire data to possibly isolate a specific cylinder fault.

Fuel System
    • Inspect for low fuel pressure. Refer to Fuel System Diagnosis .
    • Ensure each injector harness is connected to the correct injector/cylinder. Refer to Engine Controls Schematics .

Ignition System
    • Inspect 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 spark plugs
       - Cracks on the spark plugs
       - Wear
       - Improper spark plug gap
       - Burned 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.
    • Inspect the ignition coils for cracks or carbon tracking.
    • Inspect the spark plug wires for proper resistance and condition.

Engine Mechanical
    • Inspect the following conditions in engine mechanical:
       - Compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber and leaking valve seals
       - Low cylinder compression
    • Inspect the following incorrect basic engine parts:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Symptoms - Engine Mechanical in Engine Mechanical 2.2L (L43).

Additional Checks
    • Inspect the exhaust manifold for cracks or gasket leaks. Refer to Symptoms - Engine Mechanical in Engine Mechanical 2.2L (L43).
    • Inspect the following conditions for a possible exhaust leak:
       - Damaged or collapsed pipes
       - Heat distress or possible internal failure of mufflers
       - Crank signal intermittent condition
       - Possible plugged three-way catalytic converter (TWC)--Refer to Restricted Exhaust in Engine Exhaust.