Backfires

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

POSSIBLE CAUSE ACTION

Incorrect spark plug wire routing (firing order) Check firing order.



Low fuel pressure Check fuel filter, fuel pump, fuel pump relay and pressure regulator. Related Tests, Information and Procedures Also Chart A-5 Fuel System Electrical Test



Mechanical failure Perform wet and dry compression test and engine vacuum test at idle. Check for broken intake valve spring or burned valve, worn camshaft (rounded exhaust lobe), broken or severely worn rocker arm, etc. Check for burned out head gasket between adjacent cylinders.