If your vehicle is showing loud popping noise from the exhaust (backfire), here are the most likely causes and the parts you'll need to fix each one.
If a spark plug fails to ignite the fuel mixture in the cylinder, the raw, unburned fuel is pumped into the hot exhaust system where it spontaneously ignites, causing a loud pop. This is frequently caused by worn spark plugs, failing ignition coils, or crossed spark plug wires after a recent tune-up.
A leak in the exhaust manifold or piping can draw fresh oxygen into the exhaust stream between exhaust pulses. This oxygen mixes with normal unburned fuel vapors in the hot exhaust and ignites, creating a popping sound, especially when decelerating.
If the engine is running too rich (injecting too much fuel), the excess unburned fuel travels into the exhaust system and ignites. This is often caused by a failing mass air flow sensor, a faulty oxygen sensor, or a leaking fuel injector.
If the spark fires at the wrong time, or the engine's valves open out of sync, combustion can happen while the exhaust valve is open. This shoots the explosion directly into the exhaust pipe. This can happen if a timing belt is installed a tooth off or if a VVT solenoid fails.
If an exhaust valve is damaged, burnt, or has a broken valve spring, it will not seal the combustion chamber properly. The explosive force of the engine's power stroke will leak directly into the exhaust manifold, causing a loud, rhythmic popping noise.