What is an EPROM modification?

The EPROM in an ECU contains the instructions that the engine computer executes. You can consider the EPROM as the "rulebook" defining how the ECU will react to any given situation. By modifying the program in the EPROM, we change the rules by which the ECU plays. This allows us to get around some of the more bothersome restrictions the factory imposes on the ECU, while adding some really unusual functions the factory could have never foreseen.