Backfires

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

PRELIMINARY CHECKS
^ Perform the careful "Visual And Physical Checks" in Preliminary Checks. - Important Preliminary Checks

IGNITION SYSTEM
^ Check for 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. See underhood "Vehicle Emission Control Information" label.

ENGINE MECHANICAL
^ Perform a compression check and look for sticking or leaking valves.
^ Check valve timing and valve lash adjustment.
^ Check intake manifold gasket for vacuum leaks.
^ Check EGR system operation for being open all the time. Refer to Chart C-7 EGR System Check. Testing and Inspection
^ Check intake and exhaust manifolds for casting flash.