Ok guys help a newb out, I've got a 03 WRX that I want to gut and transplant in a 05 Forester XT engine (already have it) and an STI 6MT (looking for one).


So I suppose that I will need a 05 STI ECU (will a 04 ECU work?) and a wiring harnesses. Right now I’m concerned with which wiring harnesses I need to replace, as I want AVCS to work, and I don't want to cut any corners. Any advice is welcome!

do you have the 04 fxt ecu .. its good enough basicly the same hardware as an 04 sti ecu .. just differnt maps your gogin to want a reflash anyway

an 05 ecu is BAD it has the imobilizer

threre is only 1 wiring harness .. they body and engine are merged in a subaru its "pull both harness strip what you don't need then remege the harnesses" not for the faint of heart

Nope, no 04 FXT ECU, but it looks like I will be getting an 04 STI ECU. Any idea what the part number for that wiring harness is?

nop but the last time looked the big harness was over $1200

nop but the last time looked the big harness was over $1200


And that's just part of it. You would still need the "front loop" harness. The only reason you need that harness is for the two main engine connectors. But that harness is another ~500 or so. Plus you'll need the gas pedal, fuel pump controller.

Another option for you... Get a complete JDM STi Intake Manifold (Injectors, rails, sensors, solenoids, wiring harness), the AVCS wiring kit from IA Performance, and the JDM Ver 7 or Ver 8 ECU. Bolt the STI intake manifold to the 05 FXT Longblock (Just remove FXT intake manifold) That will allow you to run AVCS, but there's a possibility you won't pass emissions with that setup. I've heard mixed results with passing emissions with the JDM computers. Then to compensate for the 2.5L of displacement, you'd just have the JDM ecu reflashed.

I've heard mixed results with passing emissions with the JDM computers.

First of I live in California so emisions is rough. Second I can't risk not passing emissions, so a JDM ECU is not an option.

Anyone have part numbers for the STI wiring under the hood? Better yet, anyone have a source for them? Can I use a WRX harness?

couldn't you just do what is described here:

http://www.elementtuning.com/V8%20Install/Element%20V8%20EJ25%20Install.htm

since a fxt ej257 motor is basiclly the same as a usdm sti motor from my basic understanding.

but as far as getting AVCS to work your only option as of right now is either jdm ecu or a hydra