Backfires

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



SYSTEM OR COMPONENT TO CHECK ACTION

COMPUTER INPUTS/OUTPUTS CHECK: ^ AIR FLOW METER: Sticking or damaged
air flow meter flap
^ REFERENCE WHEEL: Missing or damaged teeth
on reference wheel
^ ENGINE SPEED/REFERENCE SENSOR: Defective,
improperly installed, or damaged engine
speed/reference sensor
^ OXYGEN SENSOR: Excessive lean air/fuel mixture






IGNITION CHECK: ^ IGNITION COIL: for proper
output voltage with diagnostic scope.
^ 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.)
^ DME CONTROL UNIT: Final output stages of
DME control unit defective.



ENGINE CHECK: ^ COMPRESSION: Perform a compression
check, look for sticking or leaking valves.
^ CARBON DEPOSITS: Heavy carbon deposits on
intake valves (most apparent during warm-up periods).
^ VACUUM LEAKS: Intake manifold gaskets and
hoses.
^ RESTRICTIONS: Intake and exhaust system for
casting flash or other restrictions.



FUEL CHECK: ^ FUEL INJECTORS: Poor
spray pattern, clogged or stuck injector.
^ FUEL DELIVERY: Check fuel pump pressure and
volume output.
^ FUEL QUALITY: Check for fuel contamination,
water, diesel, in fuel?