GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Cavalier (CNG) 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 Fuel System Unwanted Switch to Gasoline

Checks

Action

DEFINITION: During normal operation, the vehicle switches to gasoline operation when there is still sufficient CNG pressure in the tank (over 1/8 of a tank) and no malfunction indicator lamp (MIL) was displayed.

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

Sensor Checks
    • Inspect the crankshaft position sensor (CKP).
    • Inspect for an intermittent ignition input circuit to the ECU.

Fuel System Checks
    • Verify the fuel system pressures. Refer to Fuel System Diagnosis .
    • Inspect the gas distribution adapter (GDA) for leakage.
    • Inspect for an intermittent NGO enable circuit.
    • Inspect for a skewed fuel pressure sensor (FPS) reading. Refer to CNG Fuel Gauge Reading Inaccurate .
    • Inspect for a faulty mixture control valve (MCV).

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.

    • Verify the proper ignition voltage output 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 for bare or shorted ignition wires.
    • Inspect for loose ignition coil connections.
    • Inspect for loose control module or ignition system grounds.

Important: If the engine starts but then immediately stalls, remove the CKP sensor. Inspect for improper resistance or faulty connections.