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 - Engine Controls .

Ignition System Checks

    • Check for the proper secondary voltage output with a J 26792 spark tester, or an equivalent. Refer to Electronic Ignition (EI) System Diagnosis .
    • Inspect the spark plugs for correct operation and performance. Refer to Spark Plug Inspection .

Engine Mechanical Checks

    • Check for any of the following engine mechanical problems:
       - Broken or weak valve springs
       - Low compression
       - Sticking or leaking valves
       - Incorrect valve timing
       - Incorrect or worn camshaft
    • Refer to Engine Compression Test in Engine Mechanical.
    • Check the intake and exhaust system for casting flash or other restrictions.

Additional Check

Check for a leaking or sticking exhaust gas recirculation (EGR).