ive got an s5 engine running s4 electronics, the front cover was swapped to make this work and im really not looking to swap the wireing harness front cover and all the other crap that goes with it, (injectors, afm relays and sensors and such) to put this engine back on s5 electronics.
so my question is, can you pin up the wires on the s4 harness to fit the s5 plug so you can run it?

 

i beleive so

 

is there anything id need to rewire to make work?

 

just make sure all the wire are in the right spot in the plugs. thats what my friend is doing and that what i am going to do when i get my new engine.

 

There is no point in "upgrading" to the S5 ECU, it won't give you any extra performance. You'll get better self-diagnosis, emissions control and transient throttle fuelling, and if you add a bunch of extra inputs the S4 harness doesn't have you'll get better idle speed control. That's it.

 

so even though the engine is s5, theres no point in taking it off the s4 ecu?