Backfire

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


PRELIMINARY CHECKS

^ Perform the careful visual/physical checks as described at start of "Symptoms,".


IGNITION SYSTEM

^ CHECK: Proper ignition coil output voltage with spark tester J26792 or equivalent (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: Spark plug wires for crossfire, also inspect electronic ignition, spark plug wires, and proper routing of plug wires.

^ CHECK: Ignition timing. Refer to "Vehicle Emission Control Information" label.

^ CHECK: If an intermittent condition exists in the ignition system, see Ignition System.

ENGINE MECHANICAL

^ CHECK: Compression - Look for sticking or leaking valves.

^ CHECK: Valve timing.

^ CHECK: Intake and exhaust manifold passages for casting flash.


FUEL SYSTEM

^ CHECK: Perform fuel system diagnosis check, see CHART A-7.

ADDITIONAL CHECKS

^ CHECK: Exhaust gas recirculation (EGR) gasket for faulty or loose fit.

^ CHECK: EGR operation for being open all the time. Refer to "EGR," CHART C-7.

^ CHECK: Intake and exhaust manifold for casting flash.