| DEFINITION: The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise. |
| Preliminary Checks |
Refer to Important Preliminary Checks in Symptoms - Engine Controls
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| Ignition System Checks |
IMPORTANT:
A higher secondary ignition voltage is required to operate the vehicle on CNG than on gasoline.
- Inspect for proper secondary ignition system voltage output using only the J 26792
spark tester.
- Remove and inspect the spark plugs for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
- Test for proper ignition system operation.
- Test for crossfire between spark plugs. Test for spark plug wire failure. Wetting down the secondary ignition system with a water spray bottle may aid in locating damaged or deteriorated components.
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| Engine Mechanical Checks |
- Inspect the engine for the following:
- Intake manifold leaks
- Improper valve timing
- Proper engine cylinder compression
- Sticking or leaking intake or exhaust valves
- Exhaust system leakage
- Inspect the intake and exhaust system for casting flash.
|
| Fuel System Checks |
Perform fuel system diagnosis. Refer to Fuel System Diagnosis
. |
| Additional Checks |
- Review service bulletins for PCM programming updates.
- Verify that the correct CNG software and calibration has been programmed into the PCM.
- Test for proper operation of the AFO Enable circuit.
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