Section 1172 (Engine Controls - 6.0L - Alternative Fuels (Troubleshooting)): Troubleshooting: Backfire

WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Backfire

Checks	Action
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 .
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.
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.