Backfires

SYMPTOM DESCRIPTION:

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



SYSTEM OR COMPONENT TO CHECK ACTION

IGNITION
CHECK: ^ IGNITION COIL for proper output voltage
with spark tester or equivalent.
^ SPARK PLUGS. Remove spark plugs,
check for fuel fouled plugs, cracks, wear,
improper gap, burned electrodes, or
heavy deposits. Replace as necessary.
^ SECONDARY CIRCUIT. For crossfire between
spark plugs (distributor cap, spark plug
wires and proper routing of plug wires.)
^ TIMING.



ENGINE CHECK: ^ COMPRESSION. Perform a compression check,
look for sticking or leaking valves.
^ VACUUM LEAKS. Intake manifold gasket and
hoses.
^ RESTRICTIONS. Intake and exhaust system for
casting flash or other restrictions.



EMISSIONS CHECK: ^ AIR INJECTION. Faulty A.I.R. check valve.
^ EGR operation for being open all the time.