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.