Backfires

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

PRELIMINARY CHECKS
Perform the careful visual and physical checks as described in Preliminary Checks. Testing and Inspection

IGNITION SYSTEM
Check: Proper ignition coil output voltage with spark tester J26792 (ST-125).

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: Ignition system. Refer to Distributor Ignition (DI) system. Ignition System

Check: For crossfire between ignition wires (distributor cap, ignition wires, and proper routing of ignition wires).

Check: Ignition timing. Refer to Vehicle Emission Control Information label.

ENGINE MECHANICAL
Check: Compression. Perform a compression check look for sticking or leaking valves.

Check: Valve timing.

Check: Intake manifold gasket for vacuum leaks.

Check: Faulty Air Injection Reaction (AIR) check valve.

Check: EGR operation for being open all the time. Refer to Chart C-7 Exhaust Gas Recirculation (EGR) System. Chart C-7 EGR System Check

Check: Intake and exhaust manifolds for casting flash.