This feature can be programmed into the ECU on some petrol and diesel vehicles which results in a pop and bang or crackle noise coming from the exhaust system during engine deceleration. Many manufacturers already implement such a feature from factory on some performance models. The feature offers no performance advantages but does offer a sportier feel and noise.
Normally during engine deceleration the injectors are switched off to prevent fuel from entering the combustion chamber. When applying a pop and bang patch to an ECU we request the injectors to stay open for a short period of time after the throttle plate has closed. The spark timing maps are then adjusted so that the fuel is ignited substantially after TDC (Top Dead Centre). This results in fuel igniting during the exhaust stroke and creating small explosions within the exhaust system. These small explosions are what create the popping and banging noise and in some cases small flames can be seen exiting from the rear silencers.