Backfires

SYMPTOM DESCRIPTION:
Fuel ignites in intake manifold, or in exhaust system, making a loud popping noise. Check the following systems and components.



COMPUTER INPUTS/OUTPUTS
^ 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
^ 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 Digital Motor Electronic (DME) control unit defective.



ENGINE
^ 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
^ 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?