Backfires

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

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

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

ENGINE MECHANICAL
Check:
Compression - Look for sticking or leaking valves.
Valve timing.
Intake and exhaust manifold passages for casting flash.

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

ADDITIONAL CHECKS
- Check:
Intake and exhaust manifold for casting flash.