Backfires

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

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

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

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

ENGINE MECHANICAL
- Check compression - Look for sticking or leaking valves.
- Check valve timing.
- Check intake and exhaust manifold passages for casting flash.
- Check crankshaft balancer interrupter rings for bent or missing vanes.

FUEL SYSTEM
- Check Perform fuel system diagnosis check, refer to Chart A-7. Testing and Inspection
- Check Fuel injectors. Perform injector balance test, refer to Chart C-2A. Testing and Inspection