What makes the exhaust of a car sound like it’s skipping?



What I mean, is when someone puts an aftermarket exhaust on to their car and revs the engine, when it’s coming back to the lower RPMs it makes a skipping sound.

Example : https://www.instagram.com/p/CLxScV_ByYA/?igshid=1nnro6srozt34

In: Other

That’s the sound of fuel burning inside the exhaust, usually happens because the engine was tuned. Normally when the engine is decreasing the ECU doesn’t send fuel, but the tune changes this, so fuel is always sent, but it doesn’t ignite the fuel right away, so the engine still slows down, the ignition happens later so the fuel burns inside the exhaust, this is typically done in turbo cars to keep the turbo spinning even when you are decelerating, which means better performance

What LGV said, but put more briefly; unburnt fuel sent out of the cylinder together with exhaust gasses, then ignited inside the hot exhaust.