Just wanted to share my project using the Arduino Mega 2560. It reads vehicle engine sensors and inputs to the vehicle ECU. You can also use it to modify signals to the ECU. Something like a super air fuel converter. There is also remote control of vehicle functions and home automation functions when you get home and join your in-home network. Hope it's OK to post links to youtube.
Check out my talking vehicle diagnostic and tuning software (being integrated with Arduino).
Check out my car.
www.mytwinturbo.com
Check out my software archive.
www.maximusdvd.com
Thanks for looking!
Gary