Backfire

An afterfire in the exhaust is often caused by unburnt fuel. A backfire through the intake points to timing or valve problems. Some performance cars produce pops on purpose. Leaking exhaust joints can also make popping sounds when air is drawn in. A hissing or pop from the intake under load points to a valve that is not closing properly.

Unburnt fuel reaches hot exhaust parts and ignites.

Repeated backfires can damage the catalytic converter and silencer. Misfires, rich mixture and timing faults are common causes.