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 (ST-125).
^ SPARK PLUGS. Remove spark plugs,
check for wet 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.
^ For loose ground at the engine block.



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.