[WeirdAl1999]

I just bought a 1991 stealth R/T automatic with only 57k miles. Right now the car only has 3rd gear. Can I be certain this is the TCU? If so, can I drive the car in 3rd gear with the TCU unplugged while I replace the capacitors in it? My buddy has a heated shop that I want to work in while removing the TCU, but I want to be able to drive it back home with the TCU unplugged while I re-solder new capacitors on the TCU.

 

[WeirdAl1999]

I forgot to mention it also has reverse, although it shifts hard into reverse.

 

[white93gt]

Can I be certain this is the TCU? If so, can I drive the car in 3rd gear with the TCU unplugged while I replace the capacitors in it?

You can’t be absolutely certain it is the TCU, but it’s most likely the problem. Yes you can drive it with TCU unplugged, just avoid harsh acceleration from stopped position. Since you’re taking off from a stop in 3rd gear it puts a strain on clutch packs in transmission, but after about 30 mph or so it’s back to more of normal state. Just wouldn't drive it over long period of time before repairing it.

Hopefully replacing electrolytic capacitors will cure the problem. If you don’t already know capacitors are polarity sensitive, be sure to install with positive and negative legs in same position as ones removed.

 

[WeirdAl1999]

You can’t be absolutely certain it is the TCU, but it’s most likely the problem. Yes you can drive it with TCU unplugged, just avoid harsh acceleration from stopped position. Since you’re taking off from a stop in 3rd gear it puts a strain on clutch packs in transmission, but after about 30 mph or so it’s back to more of normal state. Just wouldn't drive it over long period of time before repairing it.

Hopefully replacing electrolytic capacitors will cure the problem. If you don’t already know capacitors are polarity sensitive, be sure to install with positive and negative legs in same position as ones removed.

Thank you so much for the quick response. I plan to repair it this weekend, fingers crossed replacing the capacitors will fix it.

 

[white93gt]

Thank you so much for the quick response. I plan to repair it this weekend, fingers crossed replacing the capacitors will fix it.

It did mine, but I had to also repair a burnt trace because one capacitor fried itself and brunt trace into next to it.

 

[WeirdAl1999]

Well after taking the TCU out, I found out that somebody has rebuilt it in 2019. I am not sure where to go from here. It has warranty stickers and I'm not sure whether I should try to figure out who rebuilt it, or just void the warranty and take it apart. I'm afraid that it has been like this since 2019, and that was an unsuccessful attempt to try to get it to work.

 

[WeirdAl1999]

Ok so I bit the bullet and opened it up and have discovered something odd. Anybody know what that is? doesn't seem to be a capacitor.

 

[WeirdAl1999]

Upon further analysis it appears to be a C102 capacitor I will get one tomorrow and solder it in.

 

[white93gt]

Ok so I bit the bullet and opened it up and have discovered something odd. Anybody know what that is? doesn't seem to be a capacitor.

Upon further analysis it appears to be a C102 capacitor I will get one tomorrow and solder it in.

.. WTF…. Yeah that smoked area is a problem, I had to find a picture of a 91-92 board to even figure out what was once there.

But you are correct there used to be a ceramic capacitor there (see bottom of attached picture), looks like it completely exploded which is known to happen if installed with reverse polarity. Problem is the C-102 is only the location on board, I have no idea what the micro-farad or voltage rating it would have been. You MUST have same micro-farad rating but can guess at voltage rating, I’d guess you could safely use 50 volt or higher rated one, as 50v is highest I’ve seen in the ECU or TCU.

First problem I’ve seen with a ceramic capacitor, usually all the problems are with electrolytic capacitors like ones circled in red. I didn’t even chance the yellow colored electrolytic capacitors in my TCU or for sure not the red ceramic ones.

One more thing, read bottom portion of link bellow about possible chip problems with the 91-92 TCU’s.

Transmission Control Unit (TCU) for Mitsubishi 3000GT

 

[WeirdAl1999]

I installed new caps and still... nothing. I cannot afford to buy a new TCU, anybody know any rebuilders? Or have any MD740087 for a reasonable price? I'm assuming the later 1993 TCU's don't work on mine, since they are much cheaper on ebay.

 

[white93gt]

I installed new caps and still... nothing. I cannot afford to buy a new TCU, anybody know any rebuilders? Or have any MD740087 for a reasonable price? I'm assuming the later 1993 TCU's don't work on mine, since they are much cheaper on ebay.

Only rebuilder I know is one I linked at bottom of above post #9. The ’93 and later TCU’s where 2 connector units, so they won’t work in place of your 3 connector unit.

 

[white93gt]

Or have any MD740087 for a reasonable price?

You could post in parts wanted section for one, some of the part out guys might have one that they can confirm is a working unit.

Or someone that might let you try a known good unit in your car to confirm it being the problem. You don’t have to install it to test; the connectors/wires can be plugged into unit with it resting against the trans hump on passenger side.

 

[WeirdAl1999]

You could post in parts wanted section for one, some of the part out guys might have one that they can confirm is a working unit.

Or someone that might let you try a known good unit in your car to confirm it being the problem. You don’t have to install it to test; the connectors/wires can be plugged into unit with it resting against the trans hump on passenger side.

I'll post a part wanted post. Thank you for your help, really appreciate what you're doing.

 

[white93gt]

Thank you for your help, really appreciate what you're doing.

Your welcome, I’ll edit my above post about connectors on TCU as I remembered them completely backwards, yours is 3 connector and 93-96 are 2 connector.

 

[white93gt]

I installed new caps and still... nothing.

Just thought of something since it appears your TCU exploded a capacitor, it might have also blown power fuse for it. Check to see if the 10 amp #7 fuse is not blown in under dash fuse box.

 

[jose.alonso]

I just bought a 1991 stealth R/T automatic with only 57k miles. Right now the car only has 3rd gear. Can I be certain this is the TCU? If so, can I drive the car in 3rd gear with the TCU unplugged while I replace the capacitors in it? My buddy has a heated shop that I want to work in while removing the TCU, but I want to be able to drive it back home with the TCU unplugged while I re-solder new capacitors on the TCU.

I drove mine with a bad TCM for a couple of years, even in the highway doing 80 mph never realized what was wrong with it until I found a former Mitsubishi car mechanic working at Autozone, he showed me what was wrong with my. Vehicle, he also find me a TCM from an SOHC that worked in my DOHC for 4 years, TCM is again bad

 

[WeirdAl1999]

I drove mine with a bad TCM for a couple of years, even in the highway doing 80 mph never realized what was wrong with it until I found a former Mitsubishi car mechanic working at Autozone, he showed me what was wrong with my. Vehicle, he also find me a TCM from an SOHC that worked in my DOHC for 4 years, TCM is again bad

Wow, I'm surprised that didn't cause any damage to your transmission.

 

[jose.alonso]

Am driving that car again on limp mode because of TCM but now I know better