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 Check - 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 Check - EGR