[MFFJM2]

The popping sound is the sound of afterfire or small explosions of unspent fuel in the exhaust. Afterfire occurs in engines that have an emission system malfunction (air injection system diverter valve, or pair valve), exhaust leak or unburnt fuel in an exhaust system. When a driver shifts up and lets off the accelerator, the engine has a moment of running rich or with insufficient oxygen. This causes an incomplete burn which causes the fumes to explode in the exhaust system. The marble is the best and cheapest mod to fix this problem. There is no gain or loss in Hp by doing this mod, it just stops the popping sound.