Backfires

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

PRELIMINARY CHECKS
1. Perform careful visual and physical checks as described in preliminary checks. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Preliminary Checks. Testing and Inspection

ADDITIONAL CHECKS
1. Check the Exhaust Gas Recirculation (EGR) gasket for faulty or loose fit.
2. Check the EGR operation for being open all the time. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-7. Chart C-7 EGR System Check
3. Check the intake and exhaust manifold for casting flash.

IGNITION SYSTEM
1. Check the proper ignition coil output voltage with spark tester J 26792 or equivalent (ST-125).
2. Check the spark plugs. Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.
3. Check the spark plug wires for crossfire, also inspect Ignition Control (IC) system assembly, spark plug wires, and proper routing of plug wires.

NOTE: If an intermittent condition exists in the ignition system, refer to Ignition System / Testing and Inspection.

ENGINE MECHANICAL
1. Check the compression, look for sticking or leaking valves.
2. Check the valve timing.
3. Check the intake and exhaust manifold passages for casting flash.

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