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

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.

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