GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Cavalier (CNG) 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 Backfire

Checks

Action

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

Preliminary Check
    • Refer to Symptoms .
    • Search for service bulletins.

Ignition System Checks

CNG is a gaseous fuel. It requires higher secondary ignition system voltages for the equivalent gasoline operating conditions. If a problem is reported during CNG operation but not during gasoline operation. do not discount the possibility of a CNG-only ignition system failure. Test the system accordingly.

    • Inspect for the proper ignition coil output voltage using the J 26792 or the equivalent.
    • Inspect the spark plugs for the following conditions
       - Wet plugs
       - Cracks on the spark plugs
       - Wear
       - Improper spark plug gap
       - Burned electrodes
       - Heavy deposits
    • Inspect the spark plug wires for proper resistance and condition.
    • Inspect the ignition coils for cracks or carbon tracking.
    • Inspect for loose ignition coil connections.
    • Inspect for loose engine control module grounds.
    • Inspect for loose ignition control module grounds.

Engine Mechanical Check

Important: The AF system delivers fuel to the intake system through fumigation. This method is more sensitive to intake manifold leakage than the gasoline fuel supply system.

    • Inspect the engine for the following conditions:
       - Improper valve timing
       - Engine compression
       - Manifold vacuum leaks
       - Intake manifold gaskets
       - Sticking or leaking valves
       - Exhaust system leakage
    • Inspect the EGR valve for a stuck open pintle.
    • Inspect the intake and the exhaust system for casting flash or other restrictions. Refer to Intake Manifold Clean and Inspect or Exhaust Manifold Clean and Inspect in Engine Mechanical - 2.2L in the J Platform Service Manual.

Fuel System Checks

Perform a fuel system diagnosis. Refer to Fuel System Diagnosis .

Additional Checks
    • Inspect for proper PCM software. If the incorrect PCM software is installed, incorrect timing advance will be used for bi-fuel operation. This may cause a backfire.
    • Verify that the NGO enable circuit is not intermittent. An open circuit will retard ignition timing while operating on CNG and may cause a backfire.