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).
^ 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 and ignition timing.
^ CHECK: 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.. Related Tests, Information and Procedures
^ CHECK: Fuel injectors. Perform injector balance test, refer to CHART A-7. Related Tests, Information and Procedures

ADDITIONAL CHECKS

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

ENGINE MECHANICAL

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