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· Premium Baller
94 WRX, '11 R6 race bike
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6,133 Posts
the ecu connectors won't fit, plus there is more than just the ecu that you will need from the sti. for example, the rs has a cable driven throttle and the sti's is electronic, you'd need a new setup for that as well. it makes it a lot less complicated if you just rewire the harness for the new engine
 

· Registered
99 Aspen White Coupe
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480 Posts
People do use a different ECU, in fact, you have to. An RS ECU only knows how to operate a RS engine and you need the right ECU for the right engine (this isn't purely true, but for a simple explanation, it is) The re-wiring part comes in making it work with all the other crap on your car that you can't convert.
 

· Premium Member
2002 2.5 RS-T
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3,814 Posts
yes thank you for the helpfull and not so helpfull comment. But anyways, what would be an easier swap than a 05 sti motor? would the 05 wrx motor or is it still ran by computers?
with any turbo engine you're going to need the ecu for that engine.....when swapping there really is no way around ecu swap and harness merging ;)
 

· Modsterdomus
2000 STM RS Sedan 5spd
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12,252 Posts
yes thank you for the helpfull and not so helpfull comment. But anyways, what would be an easier swap than a 05 sti motor? would the 05 wrx motor or is it still ran by computers?
I dont know of any EJ series motors NOT run by computers.

maybe pre-93? I dont knwo what subaru did before the impreza, just never cared to research it.

Chris
 

· Wiring Guru
01 RS, 97 Ducati
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418 Posts
The best way to go with a swap is to do a harness merge. Regardless of what people say swaping the whole harness in is a PITA cause you still have to merge a bunch of wires for the lights, windows doors and other stuff. I've done both and the second method flat out sucks because you have to do lots of little merges throughout the harness rather then one big merge in one place.

Z
 

· Registered
99 Aspen White Coupe
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480 Posts
Are you planning on doing this or are you just trying to learn? If you're going to do this, I'd really consider having a shop do it for you. There's a lot of confusing info in this thread, and I'm not sure you sound ready to tackle something like this on your own. However, if you're just learning, it's all good.
 

· Premium Baller
94 WRX, '11 R6 race bike
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6,133 Posts
yea it would be a bit easier if you don't have that stuff, but not that much. those sort of items don't take much time at all to incorporate back into the harness. Actually, I think that people who merge (say for an example) an 05 wrx engine harness with a 99 rs harness merge only the wires that matter for the engine and supporting accessories contained in the engine bay. If it is done right, things like doors and windows that stuff should be untouched.

if i got the wording of your original question, a newer ecu can't plug into an older harness, not only would it not fit, but as other people said, there are other things missing and if for some reason you got it to work, you would have a lot of trouble on your hands.

There is also one other option, if you can source a wrecked car, you can use the entire harness from the WRX and put it in your older impreza and splice for a couple things, like the doors, front lights, tail lights, roof lights, and dash if you keep that.
 

· Registered
2001 Subaru Impreza 2.5rs
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655 Posts
Actually, I think that people who merge (say for an example) an 05 wrx engine harness with a 99 rs harness merge only the wires that matter for the engine and supporting accessories contained in the engine bay. If it is done right, things like doors and windows that stuff should be untouched.
Its actually the other way around. Most of the engine bay stuff remains intact since you would be using the 05 ECU, you splice in the necessary dash components, etc.

OP: Check out the stickies at the top of this forum and give them a good read, they will definitely help you out.
 
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