GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1997 🢒 GMC K Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 5.0L, 5.7L, and 7.4L 🢒 Backfire

Checks

Action

Definition: The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise.

Preliminary Check

Refer to Important Preliminary Checks .

Ignition System Checks
    • Check for the proper ignition coil output voltage with the spark tester J 26792 or the equivalent.
    • Check the spark plugs.
    • Remove the spark plugs.
    • Check for the following items:
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • Check the ignition system. Refer to Enhanced Ignition System .
    • Check for crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of the plug wires). Refer to Engine Electrical.

Engine Mechanical Checks
    • Check the engine for the following the items:
       - Engine compression
       - Improper valve timing
       - Intake manifold gaskets, refer to Engine Mechanical.
       - Sticking or leaking valves, refer to Engine Mechanical.
    • Check the EGR operation for being open all the time. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .
    • Check the intake and exhaust system for casting flash or other restrictions. Refer to Engine Mechanical.

Fuel System Checks
    • Perform a fuel system diagnosis. Refer to Fuel System Diagnosis .
    • Perform a fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test .
    • Perform a fuel injector balance test. Refer to Fuel Injector Balance Test for the 5.0L, 5.7L or the 7.4L.

Additional Checks
    • Check the EGR gasket for a faulty or loose fit.
    • Check the EGR Valve operation for being open all the time. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .