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Old 06-25-2002, 05:14 PM   #1
beachbum
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Question 1.8 to 2.5- problems going to non-OBDII ECU?

Hi, everyone. I've been gone a long time... feels good to get back to the i-club. Anyway, here's the story. I've got a 1995 Impreza L that I've modded quite a bit, but still has the 1.8L. I want to swap in a 2.5L, and am totally confident that it'll work just fine... with the exception of one area. Since my car is not OBDII, but all 2.5s are (AFAIK), does anyone know what problems I'll run into trying to adapt the newer engine to the older ECU? I've seen this done (bobjr94), but his car is OBDII, I believe. My goal is to do this as cheaply as possible without sacrificing reliability.

Any ideas? I love grease and wrenches, but wires scare me.
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Old 06-26-2002, 01:45 AM   #2
Kostamojen
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I have nooooo idea... I was wondering about that too, but ive seen alot of RS ecu's around for cheap. I'd be more worried if the OBD-I would respond to the MAP sensor as opposed to the MAF sensor, but I know little about electrical techical stuffs

I was wondering if you were going to swap the tranny + diff as well... And if you were going to put in the hydrolic clutch (I'm worried if the cable clutch can work with the EJ25)
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Old 06-26-2002, 09:52 AM   #3
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There are a couple problems that I can forsee with this project. Most of them aren't specifically OBD-II specific. I have swapped a SOHC 2.5L motor in my GT (which originally had the DOHC engine) using the original ecu. I was able to use the MAF sensor from the original engine for fueling. However, the newer engine does not have provisions for an egr system - you will get a check engine light if you use the old ecu (and it was tuned for egr - don't know if it is). Doesn't hurt performance any . . .

I know OBD-I systems use a different O2 sensor set up. I'm not sure if that would be an issue or not, but if you use the original headers from your car, you might run into problems (I believe the 1.8L motors had a single exhaust port whereas the 2.5s have a dual). Something to look into.

Other than the increased displacement and the O2 sensor set up, I don't think there are any other snags.

Can the 1.8 ecu accomodate the increased displacement by providing the proper fuel mixtures?
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Old 06-26-2002, 09:54 AM   #4
2.5GT
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Actually, search for a thread under my handle entitled project frankensubie, or something along those lines. In order to perform my own swap I used parts from a 1.8L engine . . . might be helpful for your swap as well . . . sorry, I don't think there's any info on OBD systems, though.

Jason
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Old 06-26-2002, 09:59 AM   #5
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Re: using the RS ECU... I was thinking about that, but I really want as much of a plug-n-play swap as possible. If it were just a matter of swapping engines and ECUs, I'd do it in a heartbeat. It's just that I have a hard time telling my wife (only been married 3 months) I need to borrow her car because the engine's out of mine. I'm still breaking her in on this stuff.

As for the hydraulic clutch... I already have an ACT clutch in mine, and it's been working fine for many thousands of miles. If the opportunity presented itself, I would swap over, but if it ain't broke... Also, I think I'll keep the tranny and diff for now. They aren't "built up" by any means, but they are fairly low mile compared to the rest of my car. Should be able to handle 165 HP, I'd hope.

Josh
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Old 06-26-2002, 11:23 AM   #6
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beachbum, are you sure your L is OBD-I? Some MY95 Subes are OBD-II (Legacys). Lots of MY95 cars are, as the automakers were prepping for the MY96 mandate.
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Old 06-26-2002, 05:32 PM   #7
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Dont forget to get at least an RS fuel pump! (if not a better pump)
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Old 06-26-2002, 05:34 PM   #8
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Quote:
Originally posted by 2.5GT
(I believe the 1.8L motors had a single exhaust port whereas the 2.5s have a dual).
Everyone keeps saying this, but by looking under my car, the only difference I see between the 1.8 and the 2.5 is that the 2.5 headers are .25 wider in diameter... Other than that, they are identicle in apearance, including bolt holes on the block for the header.

I have been contimplating getting a stock EJ25 header (and midpipe too) and bolting it up to see if it works...
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Old 06-27-2002, 10:14 AM   #9
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I'd have to agree with you here. I've taken the exhaust off my car many times, and I can tell you for a fact that the gasket has two holes in it.

Thanks for all the advice, guys. You've given me lots to think about. I hope I can talk the wife into letting me do this some day soon.

Josh

Quote:
Originally posted by Kostamojen

Everyone keeps saying this, but by looking under my car, the only difference I see between the 1.8 and the 2.5 is that the 2.5 headers are .25 wider in diameter... Other than that, they are identicle in apearance, including bolt holes on the block for the header.

I have been contimplating getting a stock EJ25 header (and midpipe too) and bolting it up to see if it works...
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