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1991 Mitsubishi 3000GT SL
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Discussion Starter · #1 ·
Hey guys,
I have a '91 3000gt sl and it is stuck in limp mode. I have replaced the leaking capacitors on both the ECU and TCU.
I've been told I should start with a ECU replacement as it seems to be refurbished around '05.
On both boards the capacitor acid has seemed the surrounding area a bit. I believe there are even a few of the solder "solder pads/rings" (for lack of better name) have been eaten away on one side. (wonder if its possible or best for me to try to fix that...)

Both computers are receiving power, but the car isn't responding to a OBD scanner (according to mechanic). Hence maybe ECU first?
Though if I remove both computers, the car will not start, it will just repetitively fire.
Does this mean that the ECU is in fact working to some extent? or is it just that another part is just recognizing that it is plugged in and "ready" to start.

Anyways, what do you guys think the best (and cheapest) course of action would be? A "new" one, purchased online? A repair service that tests the product before sending back out? Should I start with ECU or TCU?

I would love to know some of your guys opinions and recommendations! It would help me tremendously.

Thank you guys!
 

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93 NA ATX 3000gt DOHC
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4,368 Posts
Not sure what you mean by “limp mode” as you didn’t clearly explain if you were talking about transmission not shifting or engine not starting. Limp mode with these cars mostly refers to and automatic transmission that’s hung in third gear and doesn’t shift up and down thru the gears while driving.

The mechanic you mention must not know a ’91 will not word with standard OBD scanner, the code pulling process requires the below process.

The car can’t start with ECU unplugged, but it can with just TCU unplugged. So if your main problem is engine not starting, your first attention should be the ECU or better yet first troubleshoot for some other problem that could keep engine from starting. It doesn’t sound like the mechanic you mentioned is one that could correctly troubleshoot your’91 3000gt.

As far as ECU is concerned, new one’s are no longer available so that leaves you with either a good “repair service that tests the product before sending back out” less than $300 or purchase a remanufactured unit from local auto parts for ~$300 or a used working one that’s had electrolytic capacitors replaced for ~ $200 or less.

You could post good clear pictures of ECU board here for members to evaluate your present ECU since you mention refurbished ~ ’05.
 

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1991 Mitsubishi 3000GT SL
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29 Posts
Discussion Starter · #3 ·
Yes, limp mode as in transmission stuck in 3rd. Should have specified.

I'm not entirely sure if the mechanic specifically said "OBD scanner" after the checkup, but he did say that the computers were not responding.
I wonder what was done...

Okay, so that makes sense. Didn't know that it could start up, with just with the TCU unplugged but not the ECU. For some reason I was under the impression it was either or.
Engine starting is not an issue. I was throwing it out there incase it was recognized as an issue. Now I know :)

Yeah, I'm trying to figure out my best bet for the route to go with the replacement. Any recommendations for a "best" option? is there a "go to" site that most use?

I will upload some photos as soon as I get a chance.

Really appreciate you assisting me! Thank you!
 

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93 NA ATX 3000gt DOHC
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Yeah, I'm trying to figure out my best bet for the route to go with the replacement. Any recommendations for a "best" option? is there a "go to" site that most use?

I will upload some photos as soon as I get a chance.
If your engine starts and runs normally there’s no need to post pictures of ECU board, because there’s unlikely a problem with it and it doesn’t even need TCU to be in the car to work. There’s very little communication from ECU to TCU, mostly just couple 5v pulses between the two that I’m not sure what it’s all about.

The problem is more likely with the TCU, which is a little harder to get out to take pictures of the board. As far as repair services, the only one I’m aware of that can test them is link below, also make note of bad processor chip images mentioned at bottom of that cover page.

 

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1991 Mitsubishi 3000GT SL
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29 Posts
Discussion Starter · #5 ·
Alright, so I'll definitely go with a TCU replacement/rebuild. That was my guess from the get go, but I figured I'd take the mechanics word... Guess that shows just how far a lot of the expertise for these older cars go with my mechanics in the area. Just to throw it out there, the car doesn't seem to have its electronic suspension working (not sure if that is ECU related) and the dash light for it is glitchy.

I have both the TCU and the ECU lying on the floor boards right now. I'll upload some pics for the sake of it when I get the chance. Maybe someone will spot something.
But regardless, I'll start looking around and highly consider the option you've provided.

edit: are these sellers still active? I get a 404 error when trying to view the DOHC TCUs.

Really, thanks!
 

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93 NA ATX 3000gt DOHC
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the car doesn't seem to have its electronic suspension working (not sure if that is ECU related) and the dash light for it is glitchy.
Not likely ECU related, the ECS unit has more of a chance of causing ECU problems than the other way around. The ECS unit suffers capacitor problems like most of the other electronics do (but has many more of them), many just unplug the ECS unit instead of trying to fix it.

edit: are these sellers still active? I get a 404 error when trying to view the DOHC TCUs.
o_O I don't understand this, where are you entering "DOHC TCUs" ?
 

· Senior **i.e. OLD** Member
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Bob.
 

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93 NA ATX 3000gt DOHC
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edit: are these sellers still active? I get a 404 error when trying to view the DOHC TCUs.
o_O I don't understand this, where are you entering "DOHC TCUs" ?
Ahhh….. OK @winwinwinwin try it this way, click on below link, scroll down to Mitsubishi picture click on the picture, then click on 3000GT TCM’s to get where the previous link took you to, I can’t explain why it won’t go any father. Or you could just call the phone number to see if they’re still doing Mitsubishi TCM/TCU’s.


Thanks Bob, (y)I didn’t understand that being the problem point.
 

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1991 Mitsubishi 3000GT SL
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29 Posts
Discussion Starter · #9 ·
Ahh okay. Good info, to access the ECS I'll have to cut some slits in the stripped mounting screws, seems someone tried to access it prior to me. I'll attempt to repair, worst case I'll just unplug it.

Yeah I will give them a call and see if they still offer the TCUs and TCU rebuilds. Thanks (y) (if not I'll find another seller)

So just to clarify, if the ECU is plugged in and the car starts, mean that it is likely working correctly? And that the ECU is not the cause of Limp Mode? (I ask because I wouldn't be surprised if the ECU is bad as one or two of the solder joint/rings were eaten away, and I just applied a lot of solder as a "cross my fingers" fix) I'd just imagine that the '05 rebuilt TCU would be less likely to fail than the original ECU... but maybe it was a botched fix, or wrong part. I'll go pull it now and upload some pics to see if you guy recognize anything.

Appreciate the very helpful info and patience with me lol! So nice to have a helpful community behind these cars.
 

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93 NA ATX 3000gt DOHC
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So just to clarify, if the ECU is plugged in and the car starts, mean that it is likely working correctly? And that the ECU is not the cause of Limp Mode?
Yes to both. You could infact drive the car with TCU removed, it just won't have 1st, 2nd or 4th gear. So it will be sluggish taking off from a stop until it gets to ~ 30 mph when 3rd wouldn't no longer be a strain on engine, but I wouldn't accelerate very hard from a stop as that would put extra strain on 3rd gear clutch pack.
 
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