I had a problem like this and the solution was simple i had given the ECU an accessory wire as it's ignition wire, so when i turned the key to on everything would like perfect but go to crank it the engine would just keep turning over but with no combustion as when you crank all accessory wires get turned off so it was turning off my ECU, it prbably ain't your problem but I'd just have a double check of your wiring.

cheers
damo