If your vehicle is showing popping or backfiring from the exhaust or intake, here are the most likely causes and the parts you'll need to fix each one.
Misfires allow unburned fuel to enter the exhaust and ignite, causing a loud pop. If spark plug wires are crossed after recent maintenance, the spark fires while the intake or exhaust valve is open.
Unmetered air entering the engine creates a lean mixture that burns very slowly. This slow-burning fuel can ignite the incoming air-fuel charge when the intake valve opens, causing a pop through the intake.
A leak near the engine allows fresh oxygen to be sucked into the hot exhaust stream during deceleration. This oxygen ignites unburned fuel in the exhaust, causing a popping or crackling sound.
A failing fuel pump or clogged filter can cause a lean intake backfire under load. Conversely, a leaking fuel injector dumps raw fuel into the exhaust, causing a rich exhaust backfire.
If the timing belt or chain jumps a tooth, or was installed incorrectly during recent work, the valves will open at the wrong time. This allows the combustion explosion to escape directly into the intake or exhaust manifolds.
A burnt, bent, or carbon-fouled valve will fail to seal the cylinder completely. When the spark plug fires, the combustion pressure shoots past the damaged valve into the intake or exhaust.