* Weak spark. This can be caused by a faulty spark plug, a bad spark plug wire, or a weak ignition coil.
* Retarded timing. This can be caused by a stretched timing chain or belt, or a faulty timing sensor.
* Exhaust leak. This can allow exhaust gases to enter the engine, which can cause backfiring.
* Catalytic converter failure. This can cause the engine to run too hot, which can lead to backfiring.
