Symptom Diagnosis: Backfires

If fuel is ignited in the intake manifold and a loud popping noise is heard, check the following items:

• Ensure EGR system is not open at all times.
• Check output voltage at ignition coil.
• Ensure there is no crossfire between spark plugs at distributor cap or spark plug wires.
• Ensure spark plug wires are routed correctly.
• Ensure ignition timing is correct.
• Check spark plugs for wear or damage.
• Ensure compression is correct.
• Check valve components and valve timing.