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 Diagnostic Notes.

IGNITION SYSTEM CHECKS
^ 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.
^ 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. Ignition System

ENGINE MECHANICAL CHECKS
^ Compression Look for sticking or leaking valves.
^ Valve timing.
^ Intake and exhaust manifold passages for casting flash.

FUEL SYSTEM CHECKS
^ Perform fuel system diagnosis check, refer to CHART A-7.
Related Tests, Information and Procedures
^ Fuel injectors, Perform injector balance test, refer to CHART C-2A.
Chart C-2A Fuel Injector Balance Test