Backfires

DEFINITION
Fuel ignites inside intake manifold or in exhaust system, making loud popping noise.

PRELIMINARY CHECKS
Perform the careful visual/physical checks as described in Diagnostic Notes. - Important Preliminary Checks

ADDITIONAL CHECKS
- Exhaust Gas Recirculation (EGR) gasket for faulty or loose fit.
- EGR operation for being open all the time. Refer to Exhaust Gas Recirculation (EGR) Chart C-7. Testing and Inspection
- Intake and exhaust manifold for casting flash.

IGNITION SYSTEM CHECKS
- Proper ignition coil output voltage with spark tester J 26792 or equivalent (ST-125).
- Spark plugs. Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.
- Spark plug wires for crossfire, also inspect ignition control module, spark plug wires, and validate proper routing of plug wires.

NOTE: If an intermittent condition exists in the ignition system, refer to Ignition System.

ENGINE MECHANICAL CHECKS
- Compression - Look for sticking or leaking valves.
- Valve timing.
- Intake and exhaust manifold passages for casting flash.
- Crankshaft balancer interrupter rings for bent or missing vanes.

FUEL SYSTEM CHECKS
- Perform fuel system diagnosis check, see Chart A-7. Testing and Inspection

- Fuel injectors. Perform injector coil/balance test, refer to Chart C-2A. Testing and Inspection