Backfires

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

PRELIMINARY CHECKS
Perform the "Visual and Physical Checks" as described in Preliminary Checks. Testing and Inspection

IGNITION SYSTEM
CHECK: Proper ignition coil output voltage with J 26792 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: Ignition system.
CHECK: For crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of plug wires).
CHECK: Ignition timing.

ENGINE MECHANICAL
CHECK: Compression. Perform a compression check - look for sticking or leaking valves.
CHECK: Valve timing and valve lash adjustment.
CHECK: Intake manifold gasket for vacuum leaks.
CHECK: Exhaust Gas Recirculation (EGR) system operation for being open all the time.
CHECK: Intake and exhaust manifolds for casting flash.