my guess and this is a guess is that when the ecu powers up it checks the sensors that are plugged in to it and the engine so it fan run the engine if all ok it then turns on bits (like fuel pump) to fire up the engine. the devices that it turns on have there own fuses but the input to their relays will not. so if you hear it starting things up for a split sec it is in the relay for one of these devices or the wiring, if nothing at all probably a short in the sensors. good luck.