I recently put an s4 motor into my s5 just to get it running and drive it around. it ran with my old motor but the coolant seals went out and i had this motor from my old fc. Now when i try to start it and it seems to be dumping too much fuel. Itll start and keep backfiring from all the fuel. i checked the injector and 1 of the primaries was wet at the bottom so i figured leaking injector. Ive swapped out that same injector 3 times and its still doing the same thing. Would anyone have any idea why it would be doing it on just 1 injector? Everything else is new on the car. New plugs, wires, fuel filter, fuel pump, battery, alternator.

 

if you have a direct short to ground on an injector primary trigger wire it will hold the injector open, since the power feed is constant and the ECU pulses the ground, so you could check for continuity to ground at the clip. however i find it strange you'd even be able to start the car if that were the case.

you can also strap the injectors to the rails off the block and spin the CAS with the key on and see if it is leaking or sticking with the key on.

next i'd check compression and just make sure you don't have a dead rotor.

 

ill check it today. i know the motor is still in good compression and no dead rotor.