You electronics DIY folks that enjoy Diesel engines might get a kick out of this... a Finnish gentleman used an Arduino Mega to make an ECU for his Audi 5cyl 2.5TDI engine...
Video of it running:
Web site (a bit sparse but some good info):
http://dmn.kuulalaakeri.org/dmn-edc/
(Hopefully this is not a repost
)