Backfires

Check the following:

1. EGR valve operation.
2. Ignition coil output--secondary--voltage.
3. Spark plugs, spark plug wires or distributor cap for crossfire.
4. Intermittent fault in primary ignition system.
5. Ignition timing.
6. Spark plugs.
7. Spark plug wires.
8. AIR check valve.
9. Valve timing.
10. Valve train parts--broken or worn.