Backfires

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

PRELIMINARY CHECKS
Perform the careful visual / physical checks as described in Preliminary Checks.

IGNITION SYSTEM CHECKS
- Proper ignition coil output voltage with spark tester J 26792 (ST 125) or equivalent.
- Spark plugs. Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.

NOTICE: If an intermittent condition exists in the ignition system, refer to Ignition System / System Diagnosis. Ignition System

ENGINE MECHANICAL CHECKS
- Compression Look for sticking or leaking valves.
- Valve timing.
- Intake manifold passages for vacuum leaks.

FUEL SYSTEM CHECKS
- Perform fuel system diagnosis check, Refer to Chart A-7.
Testing and Inspection
- Fuel injectors, Perform injector balance test, Refer to Chart C-2A.
Testing and Inspection

ADDITIONAL CHECKS
- Exhaust Gas Recirculation (EGR) gasket for faulty or loose fit.
- EGR operation (EGR valve open at the time). See Chart C-7. Testing and Inspection
- Intake and exhaust manifold for casting flash.