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 Diagnosis. System Diagnosis - Enhanced Ignition
^ Check for crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of the plug wires).

Engine Mechanical Checks

^ Check the engine for the following the items:

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

^ Check the Exhaust Gas Recirculation (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.

Fuel System Checks

^ Perform a fuel system diagnosis. Refer to Fuel System Pressure Test. System Diagnosis - Fuel System Pressure Test
^ 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

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