Backfires

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

Preliminary Check
Refer to Important Preliminary Checks. Testing and Inspection

Ignition System Checks

- Check for the proper ignition coil output voltage with the spark tester J 26792 or the equivalent.
- Check the spark plugs.
- Remove the spark plugs.
- Check for the following items:

- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits

- Check the ignition system. Refer to Enhanced Ignition System. System Check - Enhanced Ignition System
- Check for crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of the plug wires). Refer to Engine Electrical.

Engine Mechanical Checks

- Check the engine for the following the items:

- Engine compression.
- Improper valve timing.
- Intake manifold gaskets, refer to Engine Mechanical.
- Sticking or leaking valves, refer to Engine Mechanical.

- Check the EGR operation for being open all the time. Refer to EGR System Diagnosis. System Diagnosis - EGR
- Check the intake and exhaust system for casting flash or other restrictions. Refer to Engine Mechanical.

Fuel System Checks

- Perform a fuel system diagnosis. Refer to Fuel System Diagnosis. System Diagnosis - Fuel System
- Perform a fuel injector coil test. Refer to Fuel Injector Coil Test. Fuel Injector Coil Test
- Perform a fuel injector balance test. Refer to Fuel Injector Balance Test. Fuel Injector Balance Test

Additional Checks

- Check the EGR gasket for a faulty or loose fit.
- Check the EGR Valve operation for being open all the time. Refer to EGR System Diagnosis. System Diagnosis - EGR