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Old 08-02-2008, 09:29 PM   #1
Huffer
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Default 98 GT ECU into 96 GT?

The 96 GT requires premium fuel. The 98 GT does not.

Has anyone tried swapping the ECU's 98 to 96 to see if the 96 car will run on 87 octane?

Does anyone have a 96 GT and has it running fine on 87?
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Old 08-02-2008, 10:05 PM   #2
gtwagon941
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Isn't the fuel requirement more a factor of the ignition system than the ECU?

sorry for not really providing an answer, but rather another question...

BUMP

JS
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Old 08-02-2008, 11:49 PM   #3
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I have an ecu from a 97gt that ran 87 no problems. Let me know if you are looking for one.
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Old 08-03-2008, 07:28 AM   #4
Huffer
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Quote:
Originally Posted by legacy1907 View Post
I have an ecu from a 97gt that ran 87 no problems. Let me know if you are looking for one.
The 97 GTs ran regular gas. The 96's didn't.
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Old 08-03-2008, 09:55 AM   #5
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i guess im confused....i thought you were testing to see if running another year ecu would let you run 87 octane? i was just saying i had a 97 ecu if you wanted to try it out.
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Old 08-03-2008, 12:23 PM   #6
Jonathan
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Huffer

What you really need to do first is find a mod friendly Subaru dealer parts counter man and find out the differences in the motors between a 96 EJ25 and a 97+ EJ25 : Knock Sensours, Cam and Crank position sensours, Coil Packs, and just maybe even cylinder heads and pistons. If nothing has changed, then yes I suspect you can indeed drop in a MY '98 GT ECU into your '96 GT, although you really should also compare the wiring diagrams of both vehicles as well.

EDIT: Both the '96 and the '98 GTs in question are 4EAT automatics ? IIRC, the MY98 models had revised Transmission control (TCU) modules that improved upon the 4EATs behaviour. I am not sure if actual changes to the tranny were involved, or for that matter if the TCU is part of the ECU module or not.

Last edited by Jonathan; 08-03-2008 at 12:34 PM. Reason: More questions
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Old 08-03-2008, 12:28 PM   #7
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Quote:
Originally Posted by legacy1907 View Post
I guess I am confused....I thought you were testing to see if running another year ECU would let you run 87 octane? I was just saying I had a 97 ECU if you wanted to try it out.
legacy1907 - that was a nice offer.. However if you re-read Huffer's first post he already has an ECU from a '98 Legacy GT. He just wants to know if anyone has tried running a '96 GT that requires PREMIUM fuel with a later model ECU that doesn't require the more expensive fuel. Given the lack of responses, I will venture to guess that nobody on this board has tried doing this yet.
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Old 08-03-2008, 02:21 PM   #8
Patrick Olsen
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If the '96 has a knock sensor there's no reason you can't run 87 octane. It might pull a little more timing and sacrifice a little performance, but that's the purpose of the knock sensor.

The better question might be whether the '98 ECU will plug into the '96 wiring harness.
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Old 08-03-2008, 08:34 PM   #9
ReubenH
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Quote:
Originally Posted by Patrick Olsen View Post
If the '96 has a knock sensor there's no reason you can't run 87 octane. It might pull a little more timing and sacrifice a little performance, but that's the purpose of the knock sensor.

The better question might be whether the '98 ECU will plug into the '96 wiring harness.
Yeah, sad thing about that is it also sacrifices allot of fuel economy...

You should know this one huffer. It's a false economy, often times you'll be spending MORE by using lower octane than what you should be. Purely cause it has to pull the timing so much to prevent det, killing your economy.

I tried this a while ago, ran on 95 for a few weeks, and sure it was less expensive at the pump, but damn i had to visit it often. Switched back to good ol 98, and i was laughing, so much lighter on the gas...
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Old 08-04-2008, 09:59 AM   #10
Huffer
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I know the TCU in the 98's is separate from the ECU... it's located behind the center console. Little silver box.

Reuben - these cars are mild-mannered NA machines... not the twin turbo Japspec car you have, running on NZ 98 when it's tuned for Jap 100...

I will search around to see if I can find anyone with a 96 GT running on less than 91 R+M/2 octane (US market). If it's 89 then it'll probably be ok.
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Old 08-05-2008, 07:19 AM   #11
Huffer
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Quote:
Originally Posted by Huffer View Post
Does anyone have a 96 GT and has it running fine on 87?
I test drove a 96 GT last night. Apart from the auto binding up a little, it seems to run fine on 87. That's what the owner throws into it. No CELs, and it's got decent pickup.
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Old 08-05-2008, 10:07 AM   #12
Huffer
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WJM - thanks for all that info. I may not pick up the 96 GT until September, but when I do I will try the 98 GT ECU out and see what happens.
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Old 08-05-2008, 08:47 PM   #13
ReubenH
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Interesting indeed. There must be some wizardry in that ECU to allow the car to run lowr octane with higher compression ratio's :P



Oh and, the plural of Lego, is... Lego. ;-)
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Old 08-05-2008, 08:55 PM   #14
Jonathan
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My understanding is that even the '96 Legacy GT still had the 112 mph speed limiter in the ECU. Plugging in the later ECU takes care of that.
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Old 11-08-2008, 06:31 PM   #15
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Sorry to bring this back from the dead but I'm interested in doing this to my '96 LGT.

My understanding is that any ECU from a '97-'99 LGT will work?

I'm looking at a '97 ECU atm. All I have to do is unplug my ECU and plug in the '97, no wiring or anything?
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Old 11-08-2008, 06:54 PM   #16
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According to my understanding, yes.

best thing to do is unplug the battery for 30mins and then remove ECU, swap in new one, bolt down, recover and reconnect battery. Reprogram your radio presets and rock it out.
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Old 11-08-2008, 07:08 PM   #17
Jonathan
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The MY99 Impreza RS and Forester had the MAP sensor in place of the MAF sensor. My *guess* is thats why the ECUs from a MY99 for these models isn't compatable.
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Old 11-08-2008, 07:16 PM   #18
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Quote:
Originally Posted by Jonathan View Post
The MY99 Impreza RS and Forester had the MAP sensor in place of the MAF sensor. My *guess* is thats why the ECUs from a MY99 for these models isn't compatable.
Makes sense.

So I've been reading around and it appears the only difference between these engine's is their ECU's from '96-99.

Am I right in saying that was the only change? I mean the CR might have gone up or down a .1 or .2 but as far as the pistons cams and heads they were all the same right?
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Old 11-09-2008, 10:41 AM   #19
EastsideLegacy
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I have a 95 Legacy L, i recently had swapped in a 2.5L ej25 97, I have been running on this for a while now and seems to have no problem at all it was a plug and play type deal.

But because i never had the motor with lightweight flywheel maybe it just feels a lot better going from the 95 Ej22.

So what i would like to know is should i swap the ecu i have from the 972.5gt into the 95 just to see if it helps ?

Any input will help if there was something i should of swapped and i didn't please inform me.
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Old 11-09-2008, 01:15 PM   #20
gtwagon941
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I did the reverse swap (2.5->2.2) and the ECU's were swapable. My car ran fine on both the 98 2.5 ECU and the 97 2.2 ECU. Ultimately, I went with the 2.2 just to be "safe".

If anyone wants to buy a 98 2.5 ECU, I have one, just let me know.

J
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Old 11-09-2008, 10:42 PM   #21
winston856
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The '96 EJ25D is 155HP/140TQ, the '97-99 EJ25D's are 165HP/162TQ

I can't believe I'm going to gain 10HP and 22lb-ft of torque (or close to that anyway) just by swapping ECU's!

Nevermind, saw the part about the engine diffs.

Last edited by winston856; 01-21-2009 at 02:09 AM.
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Old 11-30-2008, 09:30 PM   #22
EastsideLegacy
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Hey guys anyone have a wiring diagram pin out and what each pin is for the 95 legacy L ecu and the 97 gts ecu plug ...like detailed description on what wire does what so i may be able to splice the two plugs and make my L run off of the GT ecu .

The only reason is because i put a 97 2.5GT motor in my legacy L and think i would really benefit from putting in the 97 gt ECU ....

but the plug that runs to the ecu doesn't have the same pin out.

http://img.photobucket.com/albums/v6...Picture001.jpg

The light blue is the GT and black is the L..

Anyone that can help me please do.. i hope i didn't confuse anyone im all over the place tonight

thank you nasioc Leggy supporters
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Old 01-19-2009, 09:51 PM   #23
kirbykirb
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Quote:
Originally Posted by Jonathan View Post
Huffer

What you really need to do first is find a mod friendly Subaru dealer parts counter man and find out the differences in the motors between a 96 EJ25 and a 97+ EJ25 : Knock Sensours, Cam and Crank position sensours, Coil Packs, and just maybe even cylinder heads and pistons. If nothing has changed, then yes I suspect you can indeed drop in a MY '98 GT ECU into your '96 GT, although you really should also compare the wiring diagrams of both vehicles as well.

EDIT: Both the '96 and the '98 GTs in question are 4EAT automatics ? IIRC, the MY98 models had revised Transmission control (TCU) modules that improved upon the 4EATs behaviour. I am not sure if actual changes to the tranny were involved, or for that matter if the TCU is part of the ECU module or not.
Trannies were changed/updated mid 97'-98 to a newer model which led to reduction in torque bind and other solenoid C issues.

So, the TCU would of course been updated.

Physically, the ECU, TCU and DME's would all be plug and play...until the newer legacy gen since then those changed from the Hitachi ECU's we have in BD/BG to whatever newer legacies used.
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Old 01-19-2009, 09:54 PM   #24
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Quote:
Originally Posted by EastsideLegacy View Post
Hey guys anyone have a wiring diagram pin out and what each pin is for the 95 legacy L ecu and the 97 gts ecu plug ...like detailed description on what wire does what so i may be able to splice the two plugs and make my L run off of the GT ecu .

The only reason is because i put a 97 2.5GT motor in my legacy L and think i would really benefit from putting in the 97 gt ECU ....

but the plug that runs to the ecu doesn't have the same pin out.

http://img.photobucket.com/albums/v6...Picture001.jpg

The light blue is the GT and black is the L..

Anyone that can help me please do.. i hope i didn't confuse anyone im all over the place tonight

thank you nasioc Leggy supporters
GT ECU will not fit a L. Different Engines, and most likley different harness.

To better differenate, get a 97 L ECU. 98+ would work to, but 97 would be the better half imo as that did not incorporate some changes subaru made.

Would be tons easier if you had a HiDASH kit, could jus update it on the fly
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