The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support JNZ Tuning
Please Support STM Tuned

98 (auto) gsx...Bad TCU? ### help

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

GSXtacy724

10+ Year Contributor
115
0
Dec 16, 2008
Sharon, Pennsylvania
Ever since I installed a newer (supposed to work) tranny in my car, my car wont start off in 1st gear, even if I manually put the car in 1st. I believe its starting off in 2nd...Is it a bad TCU? What could it be? thanks in advance guys!
 
In an auto tranny you still have a couple of "manual" gears.. 1st being one of them. And the tcu has no control over those gears.. So it's not the tcu..
 
You are in LIMP mode. Designed to protect the transmission to prevent further damage. Sounds like a bad Transmission Computer.
 
the "Transmission Computer" is the TCU right?
Bud92gsx says its NOT the TCU
 
You are in LIMP mode. Designed to protect the transmission to prevent further damage. Sounds like a bad Transmission Computer.

You have to be mistaken for hear say...If he was stuck in limp mode, the car would always start off in 3rd gear...

There should still be the following gears..P, R,D(3), manual 2nd, Manual 1st..

If your putting the car in manual 1st or 2nd, it should go into gear...

So again, I'm saying it's not the tranny control...

Why not just unplug the TCU all together and see what happens when you do...Limp mode just like GalantGreg mentioned..
 
thanks for your help guys, im gonna check into it. i'll let you know what I figure out. If the trans is a 95-96 do I need a 95-96 trans computer or will mine work?
BTW, it actually might be 3rd that the car starts off in...
 
yeah man, it is a huge dog off the line... Thanks so much Bud92 :thumb:

oh, and when I shift from park to drive/reverse it bangs into gear pretty hard
 
Pull the TCU and see if it smells funny. I highly doubt that's your problem. They rarely go bad, and when they do, the voltage regulators go out, and the 5v circuits get flooded with 12v. Pull your codes, it might be a solenoid or pulse generator. Also, even with the car in L or 2, it will still take off in 3rd if it is in limp mode.
 
ok guys, so I pulled the TCU, took it apart, and everything looked fine. Then looked at the wires going into the tranny and saw a few NOT connected to others, etc... Here's some pics, I hope it helps.
You must be logged in to view this image or video.

You must be logged in to view this image or video.

In the 2nd picture, the sensor im pointing to has a RED wire coming off its harness thats NOT connected to anything, and now that I think about it, that sensor used to have a plug connected to it but with this new tranny, the plugs did NOT match so i had no choice but to hard wire them together and was left with this wire. Anyone know where I should connect it?
The first picture has the 2 RED wires coming out of the trans, but the plug with the BLUE wires coming off are what was on the old 98 auto trans, but red on this one. I swapped the two wires so their connected to the opposite they used to be connected to.
Sorry if this is confusing, i dont know how to explain it any easier guys. Someone please help me out tho, im so lost. Makes me wonder if I got a 1g auto trans???
Thanks in advance!
 
If there is something not connected, or a wire missing or anything out of the ordinary, the TCU with throught a fault and put the car in limp mode. How long have you had this car? It could be possible that the previous owner had the car in for transmission work, and they messed up some wiring. I am just speculating at this point. It is hard to really pinpoint the exact problem. You have to actually do process of elimination.

You took the TCU out, what you want to check for is leaking capacitors there. That is usually what goes bad there. Since you had that out, take a pic of the circuit board. Let's see what it looks like.
 
It is hard to really tell from the small picture.. but is this red wire in loom with 3 other wires?

If it is, it is the wire to your tcc solenoid. Since the car is a 2g, it needs this connected, unless if it is a JDM. That wire powers the solenoid that locks up the converter in the USDM transmissions from 95-96 and 97-99. All most all JDM transmissions purchased online are from a 95ish RVR (a russian AWD suv) which did not have a lock up type converter. If you don't know for sure what transmission you have, measure from the bellhousin flange (which mates to the engine block) to the oil cooler nipples. The lock up type transmissions have an extra 1/2" compared to the non-lock ups.

I'm in the process of building some testers for people where they can just plug it into their OBD1 or OBD2 port, and it will pull the TCU codes for them. Parts from Japan just take a while. Unless someone knows where I can find the OBD1/2 male plugs with pins around the same price.

If the wire is not sharing the plug with 3 other wires, check out my website, Automatic DSM'S. Under the tech section I have wiring diagrams for the transmissions. The overhaul manual also has a trouble shooting section.
 
Yeah man, the harness DOES have 3 other wires, and im sure your right. Alot of things were different with this transmission then the stock one that blew. Such as the flex plate bolt holes, and the drives side axle did NOT just go right in like the stock one, so i kind of had to mod it to work, and now this. Like I said, the stock connector and i had no clue what to do with it, and still dont and now see its important...What should I do
 
Does the axle you are talking about happen to be the intermediate shaft? It has two bolts that hold it on to the block, and the driver's side half shaft plugs into. If it seemed like the shaft was too long, and you couldn't get it in all the way, and the bolt holes don't line up... chances are the case is for a non lock up converter. The valve body would seem to be for a lock up if it has 4 wires going to the transmission. That is odd. Can you find the other wire that the red wire needs to connect to? Reconnecting all the solenoids and resetting the tcu (by unplugging the battery) will take the car out of limp mode if that was the only thing wrong with it. If you can't find the wire, connect it to pin 1 on your TCU. Also be sure you have the TCU and not the ECU, and be sure that's what you checked when looking for electrical damage. Part number should be MD762043. Let me know if it is something different.

As pulled from my site:

You must be logged in to view this image or video.
 
Website is Automatic DSM'S

Did you try pulling codes from your TCU?

I think I might put a forum on the site so people can post their questions. Then try my best to get kiggly, high psi tsi guy, etc to join to help further.
 
I would just follow the wiring schematic I posted up above until you find your problem. Also, if your aem box is universal, you could just wire the trans to it. Also, on your aem box you are going to want to loop your transmission pins with a resistor to keep the box from throwing a code (if it is doing that).
 
Does the axle you are talking about happen to be the intermediate shaft? It has two bolts that hold it on to the block, and the driver's side half shaft plugs into. If it seemed like the shaft was too long, and you couldn't get it in all the way, and the bolt holes don't line up... chances are the case is for a non lock up converter. The valve body would seem to be for a lock up if it has 4 wires going to the transmission. That is odd. Can you find the other wire that the red wire needs to connect to? Reconnecting all the solenoids and resetting the tcu (by unplugging the battery) will take the car out of limp mode if that was the only thing wrong with it. If you can't find the wire, connect it to pin 1 on your TCU. Also be sure you have the TCU and not the ECU, and be sure that's what you checked when looking for electrical damage. Part number should be MD762043. Let me know if it is something different.

As pulled from my site:
Yes man, you are right. I have no idea whats going on with it. Will the tranny work with a LOCKING torque converter in it? Is your diag. showing pin 1 is all the way to the right (passenger side) top wire that connects into the TCU?
 
I don't exactly remember what side it is on, but it is the only red wire on the end of one of the plugs.

You will need a lock up valve body with a lock up converter, for if it doesn't lock up at higher rpms / WOT, it can burn out the clutches in the converter, and you will lose power and mpg. I'm not sure what affect the solenoid would have on a non lock up converter though, maybe excess pressure causing it to balloon. If the case is for a non lock up, and a lock up converter is in there, the converter may bottom out when the flexplate is fully flexed. This is because the lock up converters are thicker than the non lock ups. The lock up designed case have that extra half inch of clearance.

Did you buy the trans from someone? Try to contact them if you did. It almost seems like they bought a non lock up JDM trans, and installed a lock up type valvebody.
 
So I pretty much have no choice but to buy a new trans and torque converter?
I traded a evo III on here to a guy, and thats what I got.....screwed.
I dont have their number, its been over a year now
 
I don't know for sure that is the problem. I am just thinking outloud. See if you can get those measurements I asked about earlier. Go from the face of the bellhousing to the start of the oil cooler ports. I think its around 15.5" but I will need to double check before I throw numbers out for sure. I have a non lock W4A33 in the shop right now for a rebuild, so I can get a measurement tonight. Yours should be a 1/2" longer. If worse comes to worse, just connect the wire to the TCU and see if that fixes things. Just listen carefully at higher rpms to see if the converter is bottoming out.
 
ok Bender, I'll measure that tomorrow before work, and let you know. I just went out and looked and on the smaller plug for the TCU the 1st pin is Red with Gray dots, and the bigger connector its Red with a Black stripe and gray dots, or vice versa. Which should I connect my red wire to? thanks man
 
1st-4th gears are all electronically selected in this trans, the TCU does that.

Try adjusting the linkage/encoder on top of the trans. The drop-pin hole should line up with the lever in neutral. If this is wrong the tcu will make it shift all sorts of weird/inconsistent.

Kevin
 
That's a good point Kevin, but if you look closely at one of his pictures, his TCC wire isn't connected.

GSXtacy724- The bigger red wire with the black tracer is the power supply wire for the TCU. The wire you want to tie that wire to going to your valve body is the red wire on the end.

badas93tsi- The aem ems can throw certain codes if something is out of whack. If you aren't experiencing anything, and its running good, don't worry about it. Sometimes a resistor needs to be wired in on the 2g's. I will need to double check on the 1g. (It's getting confusing in here... LOL)
Also, see if you can get on a friends computer/library/school and print off the diagram. It will help greatly. You may have a wire crossed or not connected somewhere in the harness.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top