Backfires

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

PRELIMINARY CHECKS
^ Refer to IMPORTANT PRELIMINARY CHECKS.
Testing and Inspection

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

FUEL SYSTEM
CHECK: Perform fuel system diagnosis. Use CHART A-6 FUEL SYSTEM DIAGNOSIS.
Related Tests, Information and Procedures

ENGINE MECHANICAL
CHECK: Compression, valve timing, manifold gaskets, sticking or leaking valves.

ADDITIONAL CHECKS
CHECK: EGR gasket for faulty or loose fit.
EGR operation (EGR valve open all the time).
Intake and exhaust manifold for casting flash.