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. Refer to Diagnostic Charts/Chart A-6 Fuel System Diagnosis. Related Tests, Information and Procedures
CHECK: Fuel injectors. Perform injector balance test, refer to Diagnostic Charts/Chart A-7 Poppet Nozzle Diagnosis.

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.