Backfires

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

POSSIBLE CAUSES

Ignition Systems Check
- Ignition Timing.
- Output voltage of ignition coil.
- Crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of plug wires).
- Faulty spark plugs and/or plug wires or boots.

Emission Systems Check
- EGR operation (Is it open all the time?).

Engine Mechanical Check
- Valve timing (Did the timing belt slip?).
- Broken or worn valve train parts or burned intake valve(s).