GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 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 Symptoms .

Ignition System Checks
  1. Check the ignition system. Refer to Enhanced Ignition System Diagnosis .
  2. Check for crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of the plugs wires).

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.

Fuel System Checks
  1. Check the fuel system performance . Refer to Fuel System Diagnosis .
  2. Perform the fuel injector balance test. Refer to Fuel Injector Balance Test .

Additional Checks
  1. Check the EGR gasket for a problem or loose fit.
  2. Check the AIR System for proper operation (If applicable).