GM Service Manual Online
For 1990-2009 cars only

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

    • Check for the proper ignition coil output voltage with a J 26792 spark tester or equivalent.
    • Check the spark plugs for any of the following conditions:
       - Any wet or fuel fouled plugs
       - A terminal screw that is bent or loose
       - A ceramic insulator that has cracks, carbon tracking, or deposits
       - A tip insulator that has cracks, carbon tracking, deposits, or is loose
       - A center electrode that is loose
       - An incorrect spark plug gap
       - Any missing platinum pads

Engine Mechanical Checks

    • Check for any of the following engine mechanical problems:
       - Any broken or weak valve springs
       - A low compression
       - Any sticking or leaking valves
       - An incorrect valve timing
       - An incorrect or worn camshaft
       - Refer to Engine Mechanical.
    • Check the intake and the exhaust system for casting flash or other restrictions.