Engine Swap to '98 2.5L Impreza RS

[czei]

I just swapped the engine in my '93 N/A Legacy for a newly rebuilt 2.5L '98 Impreza RS engine... The only problem is I ended up using the old harness and ECU since the RS wiring harness that came with the new engine was all hacked to pieces.

Now that its running fine, I want to go back and swap the old wiring harness for the newer one and update the ECU so it'll be dyno-able. Has anyone else tried this swap? Any tips? I'm really appreciating the extra power for rallycross.

[Legacy777]

That will likely be a monumental undertaking. I don't believe the engine harness plugs are the same and if you want to use the 2.5 ECU, it's plugs are not going to be the same. You'd have to swap the entire or almost the entire chassis wiring harness to do, and since the ECU is at different locations, you'd still end up having to do some custom wiring.

If it were me, I would try and make an adapter harness that would plug into the existing ECU connector in the Legacy and then plug into the 2.5 ECU. I know it's a little tight under the dash, but I think that's going to be your best approach.

[czei]

That will likely be a monumental undertaking. I don't believe the engine harness plugs are the same and if you want to use the 2.5 ECU, it's plugs are not going to be the same. You'd have to swap the entire or almost the entire chassis wiring harness to do, and since the ECU is at different locations, you'd still end up having to do some custom wiring.

If it were me, I would try and make an adapter harness that would plug into the existing ECU connector in the Legacy and then plug into the 2.5 ECU. I know it's a little tight under the dash, but I think that's going to be your best approach.

That's a great idea! The wiring harness is just wires, after all; the main goal is to get the 2.5L ECU working. Some sort of piggy-back adapter would probably be best so I could keep the original ECU in there in case I screw it up on the first (or second) try.

Of course if I actually want to do stuff with the new ECU it'll need an ODB port somewhere....

Thanks so much for the advice.

[Legacy777]

I would recommend trying to use the new ECU, I think you'll have more tuning options. It may require a little more work compared to a piggy back, but I think in the end you'd be happier, (assuming you can tune the stock ECU). Other thing, you may run into a few things where you may need to add or change a sensor. So you'll have to look at all those variables, but between that and a piggy back, you have some options to work with.

Glad to help.

[wtdash]

Hi,
I know this thread is getting old, but I'd highly suggest you do some research on that '98 ECU - if you haven't already.

I had a '98 Forester that used that same ECU and engine - It was the last year of the Phase I EJ25 DOHC and ECU, and there was nothing that could be done to the ECU 'as is', and couldn't find any software to connect to the ECU, other than to read basic OBD2 info. In '99 the Phase 2 RS ECU had more options for external programming/etc.

I ended up using a Greddy Emanage Ultimate - a piggy-back EM, which I don't recommend unless you know a tuner and/or have lots of $$ to get it tuned...or smart enough to do it yourself.

If you still have the stock ECU you might be able (heard conflicting info) to use the REVSCAN software* and an EVOscan cable (or make your own) to get the basic ECU info from the Select Monitor port.


GL,
Td


*This site is no longer supported but seems to be accessible @ the 1st of the month when the 'bandwidth limit' gets reset. I have the software if you have a cable.

[Legacy777]

I need to try and get on there at the first of the month to copy everything over so I can host it. Someone sent me a copy of the site, but not everything was there, and the internet archive kind of screwed with the html.

[czei]

... I had a '98 Forester that used that same ECU and engine - It was the last year of the Phase I EJ25 DOHC and ECU, and there was nothing that could be done to the ECU 'as is', and couldn't find any software to connect to the ECU, other than to read basic OBD2 info. In '99 the Phase 2 RS ECU had more options for external programming/etc.

I ended up using a Greddy Emanage Ultimate - a piggy-back EM, which I don't recommend unless you know a tuner and/or have lots of $$ to get it tuned...or smart enough to do it yourself.

Thanks for the info! It sounds like its not worth the trouble of upgrading the ECU then. Is that right? The reason I was considering it was I thought the newer ECU would give me more tuning options, but you're saying that's not the case so there's no point.

[wtdash]

Thanks for the info! It sounds like its not worth the trouble of upgrading the ECU then. Is that right? The reason I was considering it was I thought the newer ECU would give me more tuning options, but you're saying that's not the case so there's no point.

In my experience, it's not really a choice...there are no upgrade options for the '98 RS ECU, other than adding a piggy-back EM system, such as the Greddy I mentioned....and I did that to control the bigger injectors, timing, etc. w/the turbo I'd installed.

And for all the work, you're not likely going to to gain much.

Look on RS25.com for hints on what to do with your car. For Autox, you want to likely keep the torque, and you can put in Delta cams - but 4x$$ adds up.

TD