Backfires

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

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

IGNITION SYSTEM
Check: Proper ignition coil output voltage with spark tester J26792 (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 wires for crossfire. Also inspect distributor cap, ignition wires, and proper routing of ignition wires.

Check: Distributor vent system. Refer to Chart C-4C Distributor Vent System Check. Chart C-4C Distributor Vent System Check

NOTE: If an intermittent condition exists in the distributor ignition system, refer to Chart C-4A Distributor Ignition System Check. Chart C-4A Distributor Ignition System Check

ENGINE MECHANICAL
Check: Compression -- Look for sticking or leaking valves, worn camshaft lobe.

Check: Valve timing.

Check: Intake and exhaust manifold passages for casting flash.

FUEL SYSTEM
Check: Perform fuel system diagnosis check. Refer to Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

Check: Fuel injectors. Perform injector balance test. Refer to Chart C-2A Injector Coil Test Procedure and a Tech 1 scanner. Chart C-2A Injector Coil Test Procedure

ADDITIONAL CHECKS
Check: Exhaust Gas Recirculation (EGR) gasket for faulty or loose fit.

Check: EGR operation for being open all the time. Refer to Chart C-7 EGR System Check. Chart C-7 EGR System Check

Check: Secondary air injection system. Refer to Chart C-6 Secondary Air Injection System Check. Chart C-6 Secondary Air Injection (AIR) System Check

Check: Intake and exhaust manifold for casting flash.