Hi first post on this site so take it easy on me lol.
Im working on a buddys car he put a jdm sti ej20 in his wrx and it would start. im mostly looking for a link to a thread that would be the most insitefull.
He used his oem wire harness and intake manifold on this new motor since the sti ecu that came with the swap would not plug into the harness, so i kind of stepped in halfway and left to figure it out. and info on this swap and how in depth it goes would be awesome.
I have done this swap, but I had the JDM engine harness. It plugs into the USDM harness just fine, and everything works except AVCS (for v7-9). Besides the lack of some emissions crap, that is the only difference (in wiring); USDM has TGVs and JDM has AVCS (again, for v7-9).
Question: did you delete the TGVs? If you are using a JDM ecu, you MUST delete the TGVs. We need more info: what year is the WRX, what car is the 207 from, what was included with the engine, etc.
and even if your motor has the AVCS you don't necessarily need the JDM ecu, you can just hook the motor up to your USDM Harness and it will run permanantly in AVCS high lift mode and then just get a tune for some TGV deletes and you'll be fine, or another option would be to go with a standalone that has AVCS capability such as an AEM EMS or the Hydra EMS this would let you use your existing wiring harness with slight modification or you could always try and source a JDM harness which is a task in and of itself if it didn't come with the swap (I know lol i tried to get one after mine didn't come with it so I just ended up using the 207 short block with some built 205 heads) and then just use the JDM ECU
basco is spot on; however, I will add this. If you decide to go standalone, wait on it. Make sure everything is running properly with a USDM (or JDM) ECU first, and then switch it out. If you don't have the JDM engine harness, you could possibly make your own if you can get your hands on one from an early USDM STI harness. I believe the AVCS plugs (sensors and solenoids) from 04-05? STIS (04 for sure) are the same. The later STIs have the cam sensor integrated with AVCS.
The plugs are the same but the wiring is not in the same order you would need to get a schematic for both the USDM and JDM STi and use a de-pin the plug and re-order them, you could also manipulate your current harness it is only four extra wires I believe. But I would never recommend cutting up a harness.