Backfires

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

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

ADDITIONAL CHECKS
^ Exhaust Gas Recirculation (EGR) gasket for faulty or loose fit.
^ EGR operation for being open all the time. Refer to Diagnostic Charts / C Charts / Chart C-7 EGR System Check. Chart C-7 EGR System Check
^ Intake and exhaust manifold for casting flash.

IGNITION SYSTEM CHECKS
^ 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.
^ Spark plug wires for crossfire, also inspect ignition control module, spark plug wires, and validate proper routing of plug wires.

NOTE: If an intermittent condition exists in the ignition system, refer to "Ignition System".

ENGINE MECHANICAL CHECKS
^ Compression - Look for sticking or leaking valves.
^ Valve timing.
^ Intake and exhaust manifold passages for casting flash.

FUEL SYSTEM CHECKS
^ Perform fuel system diagnosis check, see Diagnostic Charts / A Charts / Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures
^ Fuel injectors. Perform injector coil / balance test, refer to Diagnostic Charts / C Charts / Chart C-2A Fuel Injector Test Procedure. Chart C-2A Fuel Injector Balance Test