Backfires

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



SYSTEM OR COMPONENT TO CHECK

COMPUTER INPUTS/OUTPUTS

CHECK:
- AIR FLOW SENSOR POTENTIOMETER: Damaged or defective
- THROTTLE VALVE SWITCH: Improperly adjusted damaged or defective.
- DIFFERENTIAL PRESSURE REGULATOR: Improper signal, damaged or defective regulator.
- OXYGEN SENSOR: False rich indication, excessive lean air/fuel mixture.
- CONTROL UNIT: Supply voltage, poor ground, defective control unit

Refer to COMPUTRES AND CONTROL SYSTEMS.






IGNITION

CHECK:
- IGNITION COIL: Check ignition pattern and sparking 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.
- IGNITION SECONDARY: Check for cross-fire between spark plugs (distributor cap, spark plug wires and proper routing of plug wires.)
- CONTROL UNIT: Final output stages of control unit defective.
- IGNITION DISTRIBUTOR, CAP, AND ROTOR: Check for cracks, arcing, moisture, rust deposits or high resistance through rotor.

Refer to IGNITION SYSTEM.




ENGINE

CHECK:

- COMPRESSION: Perform a compression test. Check for sticking or burned valves.
- VACUUM LEAKS: Check intake manifold gaskets and hoses.
- RESTRICTIONS: Check intake and exhaust system for casting flash, damaged tubing, or other restrictions.




FUEL SYSTEM

CHECK:

- FUEL INJECTORS: Poor spray pattern, clogged or stuck injector.
- FUEL DISTRIBUTOR: Sticking or damaged control plunger, mini filter in fuel inlet banjo bolt plugged or restricted.
- FUEL DELIVERY: Check fuel pump pressure and volume output.
- FUEL QUALITY: Check for fuel contamination, water, diesel, in fuel?