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So what would be the obstacles faced if I were to attempt to install an 04 STi ECU in my 91 SS?

Obviously I'd need the STi ECU and ECU connector(s) but what else would I have to change?

Did Subaru change the types of sensor outputs? I'd be using DOHC heads on the engine from either a 2.5 RS or STi (depending on what's available first) so that would take care of the cam sensor. Map sensor different?
I could eliminate my MAF.
Knock sensor signal should be the same.
CPS different?
Were 04 STi's fbw or still cable controlled on the TB?
So TPS? Throttle body swap with sensor?

Would a regular WRX ECU be better that had a traditional cable controlled TB?

Would I be best off getting an entire WRX wiriing harness and gauge cluster and swapping that in?

Basically what I'm after is an ECU that I can reprogram without having to use any additional EM. I know many of you are convinced that stand-alones are the best way to go but at what cost? What stand-alones are out there that do absolutely everything we need without costing $2000+ to have fully up and running (including WBO2's and guages etc)?

I can buy an STi ECU for less than $200. I can also buy a wiring harness for about $200 (no cluster, just engine to ECU)

So that would mean having the basics in place for around $500 after swapping in a few sensors. After that it's get the software and cables and start programming (well...learning how to program).

Any thoughts or prior experience on this?

You would need all matching stuff. Phase 2 cam and crank sensors, fuel pump crontroller, maf sensor, and a bunch of other stuff. The merging the wiring harnesses isn't for the faint of heart either. Don't get me wrong, plenty of people do it. Just don't expect to bang it out in a weekend.


I know there is a bunch of other stuff I'm missing, but you get the idea. As far as the ECU knows, it has to be to spec. Ya you can turn off CEL's from missing TGV's and stuff, but it takes almost everything to keep it happy.

Whether or not the knock censor will work is a wash. They all don't have the same signal either. Ever heard of phantom knock? People get it on 2.5 swapped WRX's. Each motor is going to sound different.

Ever come across this post at NASIOC?

How to splice in an E-Manage Ultimate

The act of wiring it in is the least of my worries. That splice-in is not the absolutely neatest work I have ever done but it sure has remained effective.

I'm one of those guys that could bang out the ECU wiring in an afternoon so long as I knew the old and new pin-outs. That's talking cut, soldered, heat-shrinked, and re-taped in about 4 hours. I spent 3 out of my 4 years in the USCG as an electronics tech. repairing radios and radars. I also worked in several electronics related industries for about 4 years after the USGC.

Swapping sensors might take some extra time.

I thought the fuel pump was on an on/off relay where it got a signal from the ECU and turned on when the relay was on (key in) and off when power was removed. A bigger fuel pump is planned anyways (Walbro).

Good luck with that...

On the topic of drive-by-wire...

Do you really need this for an STi ECU? Correct me if I'm wrong but isn't the ECU merely concerned with the throttle position and not how it got there? In other words; the dbw system is merely a motor in place of a cable. The throttle plate opens and closes and the TPS sends a voltage to the ECU without regard to how that plate got to the position it is in.

Hopefully somebody with much more knowlege on how the fbw system interacts with the ECU can chime in here.

Guys that do it for a living take about 15-20hrs to do it properly. And they do it every day.

You are underestimating the amount of work that actually has to be done to make it work. How fast can yo pull most of the tape of the harness? lol





There's a reason places like Garage Tuning charge about $1000 for merge two harnesses together. They have the pins memorized for certain cars too. Its just a time consuming process, no matter how qualified you are.



It's not just a "splice in" affair either. You need to actually merge two complete harnesses together. From the radiator fans to the fuel pump all needs to be messed with. An Emanage is small potatos, frankly. Any piggy back is.




All the newer cars have a fuel pump controller that varies the voltage to the pump. If you want to run the newer ECU, you're going to need it. I have my doubts about an STi ECU anyways. It's designed to use the cam phasing (AVCS), and being without it will present a problem.




Have you looked at the MAF-Translator Pro like I mentioned on d-sce?

Amd no, the pedal is connected by wires to the ECU, which controls the throttle. There is logic behind the ECU's control of the throttle.


If you really want to go for it you would probably be better off with a WRX ECU.

Thank you for the input. That's just what I wanted to hear.

The EMU was all of 1.5 hrs of splicing time and would have been less if my leg hadn't kept falling asleep.

So next I will turn to the WRX ECU and go from there.

I was thinking as I was writing and in the midst of it all was beginning to realize that the WRX harness and ECU would be better especially since the TB is similar.

I still have not ruled out stand-alones but I'm just trying to balance how best to spend my money vs my time.

That's pretty interesting about the STi throttle control. Was AVCS in the 04 STi?

It can be done. I'll post the write up when It drives.

PhilSine wrote:Thank you for the input. That's just what I wanted to hear.

The EMU was all of 1.5 hrs of splicing time and would have been less if my leg hadn't kept falling asleep.

So next I will turn to the WRX ECU and go from there.

I was thinking as I was writing and in the midst of it all was beginning to realize that the WRX harness and ECU would be better especially since the TB is similar.

I still have not ruled out stand-alones but I'm just trying to balance how best to spend my money vs my time.

That's pretty interesting about the STi throttle control. Was AVCS in the 04 STi?

Yes the '04 had AVCS.



Using the WRX ECU is quite common. I'd try to use a 32 bit ECU.

Also....if you go with anything newer then 04, you have to deal with the ECU requiring a chip from the key for anti-theft.