Backfires

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

Preliminary Checks
^ Perform the visual/physical checks as described under Diagnostic Notes in this section.
^ Perform visual/physical checks.

Ignition System
^ CHECK: Proper ignition coil output voltage with J26792 or equivalent.
^ 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 distributor cap, spark plug wires, and proper routing of plug wires.
^ CHECK: Ignition timing. Refer to "Vehicle Emission Control Information" label.

Engine Mechanical
^ CHECK: Compression - look for sticking or leaking valves.
^ CHECK: Valve timing.
^ CHECK: Intake and exhaust manifold passages for casting flash.

Additional Checks
^ CHECK: Intake and exhaust manifold for casting flash.
^ CHECK: EGR operation, (California Emissions only).