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. Testing and Inspection

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 the ignition system and ignition timing, refer to Distributor Ignition System Check. System Check - Distributor Ignition (DI)
^ Check the spark plug wires for crossfire, also inspect spark plug wires, and proper routing of plug wires.

ENGINE MECHANICAL
^ Check the compression and look for sticking or leaking valves.
^ Check the valve timing and manifold gaskets.
^ Check Exhaust Gas Recirculation (EGR) operation for being open all the time, refer to EGR System Check. System Check - EGR
^ Check intake and exhaust manifold passages for casting flash.