Engine Backfires

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

CAUSE (BY SYSTEM/COMPONENT):

IGNITION SYSTEMS
- Ignition Timing.
- Output voltage of ignition coil.
- For crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of plug wires).
- For faulty spark plugs and/or plug wires or boots.

EMISSION SYSTEMS
- EGR operation for being open all the time.

ENGINE MECHANICAL
- For proper valve timing.
- Broken or worn valve train parts or burned intake valve(s).