We took a unit from TDI tuning to try out on our Audi A6 Allroad 3.0 TDI and took it to a rolling road to see if these tuning boxes live up to the hype. A tuning box sits between the engine sensors and the ECU and takes the readings provided by the sensors and manipulates these before they go to the ECU. It then alters the output commands that would come from the ECU and takes over controlling the various engine components to give more power.