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1994 Diamante LS 6G72 DOHC
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Discussion Starter · #1 ·
The TCU caps are also prone to failure? :rolleyes: I just saw that mentioned in another old post from like '09 as well. Any other modules that have crappy capacitors?
My trans is just hesitant to downshift. Likes to stay in 3rd rounding corners at 5 MPH. RARELY goes to second gear unless I am 50%+ on the throttle. I have to come to a dead/complete stop to get first gear or smash the pedal <5MPH
PWR mode is slightly better, but only by a bit. I feel like that's a lot of lugging the engine and significant wear on the trans
Even upshifts feel mildly aggressive. I would think that some decent throttle would let me wind it out a little bit, but it always wants to shift at no more than 3K unless I am HEAVY on the gas

The previous owner siliconed a wire connector near the large black plastic cap of the transmission. I'll go get a picture shortly. Sorry I'm not familiar with the tranny parts, but would anything in this wire be part of the problem? Or should I just go straight to the TCU to look for cap damage?
 

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93 NA ATX 3000gt DOHC
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The TCU caps are also prone to failure? :rolleyes: I just saw that mentioned in another old post from like '09 as well. Any other modules that have crappy capacitors?
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The previous owner siliconed a wire connector near the large black plastic cap of the transmission. I'll go get a picture shortly. Sorry I'm not familiar with the tranny parts, but would anything in this wire be part of the problem? Or should I just go straight to the TCU to look for cap damage?
Yes TCU capacitors are prone to failure. As well as in tach, digital climate control and electronic controlled suspension unit.

If siliconed spot is just forward of dipstick, that would be were the four TCU solenoid wires enter transmission. If any of those wires are broke or shorted to ground you’d have a bigger problem. So I suspect TCU is most likely with other possibilities being pulse generators, even less likely vehicle speed or TPS input.
 

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The TCU caps are also prone to failure? :rolleyes: I just saw that mentioned in another old post from like '09 as well. Any other modules that have crappy capacitors?
My trans is just hesitant to downshift. Likes to stay in 3rd rounding corners at 5 MPH. RARELY goes to second gear unless I am 50%+ on the throttle. I have to come to a dead/complete stop to get first gear or smash the pedal <5MPH
PWR mode is slightly better, but only by a bit. I feel like that's a lot of lugging the engine and significant wear on the trans
Even upshifts feel mildly aggressive. I would think that some decent throttle would let me wind it out a little bit, but it always wants to shift at no more than 3K unless I am HEAVY on the gas

The previous owner siliconed a wire connector near the large black plastic cap of the transmission. I'll go get a picture shortly. Sorry I'm not familiar with the tranny parts, but would anything in this wire be part of the problem? Or should I just go straight to the TCU to look for cap damage?
I agree with @white93gt about pulling the TCU and doing at least a visual inspection of the circuit board, the capacitors, and for other burned/melted components. If you haven't set your TPS since you bought the car, you need to do that next as it can cause your exact symptoms....be sure to use the 0.025" feeler gauge spacer when setting it.
Drive car till fully up to temp, put on E-brake, shift into neutral, then pull the tranny dipstick to check level, fluid color, and smell if burnt smell there.
I have followed all your posts, pics, vids and remember some specific facts that I think may be contributing to this issue. Unfortunately, I have more things for you to strongly consider, but don't have answers. While your 94 Diamante is like our 6G72 DOHC/Cali 3000GT cars, it has some unique features that make a difference with your shifting issues. IIRC your car has a traction control system that we don't have. Your ECU is different and has the traction controller (TC) incorporated inside the ECU on a large second circuit board that communicates back/forth only through the ECU board. To complicate it further, IIRC the car has ? wheel speed sensor issues that required you to disable the whole TC system and ABS system, their fuses, ?connectors, ?vacuum lines, ?TC vacuum control solenoid and TC vacuum valve itself. In your first vid. there was ongoing screeching and ticking from one of those units and solenoids, and you are still getting code 71(TC related). I am completely lost on how the TC,TCU, ECU, and ABS inter-communicate. Normally at start-up the ECU quickly does a quick activation of the solenoids, motors, actuators in these systems to confirm their function for safety. I don't know what kind of safety adjustments occur when they detect problems. I do know that other make/models with similar TC systems, change the tranny shifting RPM points in response to such faults....like putting tranny into "granda-mode" instead of full 3rd gear only limp mode we know about when the TCU detects specific faults. If you get good info and get it sorted out, teach us. Sorting out and fixing a wheel speed sensor would be a lot easier and safer than a can of computer worms???
After driving it and before turning the key off, try grounding OBD pin 6 to CEL blink out any pending tranny codes....same as you have been doing on pin 1 to get the 62 and 71 codes.
 

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Discussion Starter · #4 · (Edited)
Yes TCU capacitors are prone to failure. As well as in tach, digital climate control and electronic controlled suspension unit.

If siliconed spot is just forward of dipstick, that would be were the four TCU solenoid wires enter transmission. If any of those wires are broke or shorted to ground you’d have a bigger problem. So I suspect TCU is most likely with other possibilities being pulse generators, even less likely vehicle speed or TPS input.
Oh joy. Thankfully no ECS and our climate controls are a little different. Not sure on that. I'd have to dig it out of the dash when I eventually upgrade the stereo this spring.
Where are these pulse generators? I see people talking about them, but can't find their location.
The only gear that really gives me a minor issue shifting is the 3-4. If under 15% throttle or so, the shift is VAGUE and jumps a little. It acts like it's in final gear and starts to slip down to a lower RPM, but then bangs it into the next gear. Not harsh, just a minor jolt. I'll try to capture it. I usually just go a little harder into the throttle in third gear and it shifts normally.

Here are the pictures I grabbed this evening.

I've been staring at some witness marks on the TPS where someone had taken it off before.

I agree with @white93gt about pulling the TCU and doing at least a visual inspection of the circuit board, the capacitors, and for other burned/melted components. If you haven't set your TPS since you bought the car, you need to do that next as it can cause your exact symptoms....be sure to use the 0.025" feeler gauge spacer when setting it.
IIRC your car has a traction control system that we don't have. Your ECU is different and has the traction controller (TC) incorporated inside the ECU on a large second circuit board that communicates back/forth only through the ECU board. To complicate it further, IIRC the car has ? wheel speed sensor issues that required you to disable the whole TC system and ABS system, their fuses, ?connectors, ?vacuum lines, ?TC vacuum control solenoid and TC vacuum valve itself. In your first vid. there was ongoing screeching and ticking from one of those units and solenoids, and you are still getting code 71(TC related). I am completely lost on how the TC,TCU, ECU, and ABS inter-communicate. Normally at start-up the ECU quickly does a quick activation of the solenoids, motors, actuators in these systems to confirm their function for safety. I don't know what kind of safety adjustments occur when they detect problems. I do know that other make/models with similar TC systems, change the tranny shifting RPM points in response to such faults....like putting tranny into "granda-mode" instead of full 3rd gear only limp mode we know about when the TCU detects specific faults. If you get good info and get it sorted out, teach us. Sorting out and fixing a wheel speed sensor would be a lot easier and safer than a can of computer worms???
After driving it and before turning the key off, try grounding OBD pin 6 to CEL blink out any pending tranny codes....same as you have been doing on pin 1 to get the 62 and 71 codes.
The trans fluid is 5 years old and around 20K, but looks and smells good.

I am unsure of the ECU differences as well. We are going on a trip late February to visit some family, so I'm hoping to send off the ECU/TCU get them recapped to be safe. I may grab a $30 TCU off eBay just to try that before $250+ computer repairs.
I'll have to look into the TPS proper setting. I knew that came into the calculations.
The ABS system was disabled by the previous owner. He had a brake/ABS light show up on the dash. The shop replaced the wheel sensor but the light persisted. They checked all other sensors with a voltmeter, but couldn't find a fault. I assume the owner declined any further diagnosis/work, as unplugging the ABS box disables the system, so no more light on the dash

The CEL codes are quite rare. They never show up on a cold start. Only when fully warm and short stops. So if I drive for 15 minutes, hop out for 2-3 minutes, and back in the car, the CEL will come on after 30 seconds. This only happens perhaps 2-3x per month. Half the time, it goes back out a few minutes later. It's very strange.
Might it be worth a shot to plug in the ABS module and see what happens? A replacement is only $20 on eBay, so I might give that a try. That noise is the ABS pump behind the headlight. It makes a mild grinding noise that sounds extremely similar to a starter not disengaging. Like you say, the ECU may be trying to prime the pump via the ECU's TCL controller.

I found a 3000gt mechanic nearby that I'm going to have pressure/smoke test for vacuum leaks. If he feels like he can take on something like this, it may be worthwhile. There is also a reputable vehicle electronics shop that my family has known for 20+ years. He might be a good resource for electrical oddities in the systems.

I'm doing the plugs and wires in ~10 days just to be sure that's not causing my very minor power loss and misfire. I dropped one of the plugs when inspecting the car and caved in the ground electrode. Perhaps I damaged the ceramic core or electrode?? I regapped it to .43 so it seemed fine. With that done and the pressure test passed, I'll probably live with it for the next 50K til the TB is due again.

There are 2 OBD style connectors down there. I'll try to find the proper pin tomorrow and report back.

PS Moths, the forum has taken away my ability to like your posts. Guess I gotta spread the love around some more before I can give you another.
 

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93 NA ATX 3000gt DOHC
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Where are these pulse generators? I see people talking about them, but can't find their location.
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Here are the pictures I grabbed this evening.
Pulse generators location on outer edge near right strut tower and that picture of silicone is where solenoid wires enter transmission. There's a rubber sealing boot there, that must have been leaking or damaged.

 

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1994 Diamante LS 6G72 DOHC
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Discussion Starter · #6 ·
Pulse generators location on outer edge near right strut tower and that picture of silicone is where solenoid wires enter transmission. There's a rubber sealing boot there, that must have been leaking or damaged.
Thanks for the pic. I'll see if those are in a similar location on mine. So the solenoid wires just go straight into the tranny? No connector or anything that may have cracked and they did this to hold it in place? That's what I was assuming. Hot engine bay plus 30 year old plastic isn't a good mix.

Also, without this fancy wiring harness, can I just probe the back of the harness with a sewing needle or similar?

 

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Thanks for the pic. I'll see if those are in a similar location on mine. So the solenoid wires just go straight into the tranny? No connector or anything that may have cracked and they did this to hold it in place? That's what I was assuming. Hot engine bay plus 30 year old plastic isn't a good mix.

Also, without this fancy wiring harness, can I just probe the back of the harness with a sewing needle or similar?
The wires do go straight into tranny at point of the silicone glob, to the solenoids mounted on valve body. There should be a square 4 pin connector ~ a foot or two before entering tranny. When new solenoid pack is purchased it comes with wire pigtail attached to solenoids, the sealing boot on wires and connector half at end of wires. When removing valve body, you unplug connector, free sealing boot by pushing it inward (inside tranny) allowing the square wire end connector to then pass thru large hole in tarnny (where boot was) and come out with valve body thru pan opening.

I don’t see why you couldn’t back probe TPS connector when checking output voltage. I’ll just point out when setting the closed position switch with connector unplugged, be sure to use an analog meter as shown and don’t forget the feeler gauge as @mothsmoths pointed out.
 

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Yeah, I'm finding that because my digital only refreshes every half to full second, accurate readings are a total PITA
Yeah, the digital units are good for accurate readings but go crazy with pulsing voltages and at times when you don’t want to sensitive ohm readings, making it hard to determine changes in continuity accurately. That’s why they show analog meter when setting the TPS closed position switch.
 

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Discussion Starter · #11 ·
I'll ground pin 6 after I take the car to town tomorrow. If I can find an analog meter, I'll probe the TPS. I grabbed some Diamond SPII a few weeks back with intentions to change the fluid. Only 20k miles on it, but it's quite a few years. I have a little extra, so here's a question:

Can I use the SP-II in the power steering? I put some Prestone garbage in there when I bought the car not knowing it was supposed to be Dex. Need to flush it before it does any damage. Replacing the pump looks like a real chore where it's positioned.
 

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I'll ground pin 6 after I take the car to town tomorrow. If I can find an analog meter, I'll probe the TPS. I grabbed some Diamond SPII a few weeks back with intentions to change the fluid. Only 20k miles on it, but it's quite a few years. I have a little extra, so here's a question:

Can I use the SP-II in the power steering? I put some Prestone garbage in there when I bought the car not knowing it was supposed to be Dex. Need to flush it before it does any damage. Replacing the pump looks like a real chore where it's positioned.
I'm about to head out for the day, so I'll write more later. But I wanted to let you know that I just saw your TPS pic from a few posts back, and its looks like the the connector to the TPS is not on all the way. I'll post your pic below and then a second pic of a properly seated one.The yellow shows how far backed off it is. The red arrow is where the TPS tab should be seated but yours isn't there and is on the wrong side of the U retainer clip. Also, the pink bolt is generally near the middle of the adjustment slot when the closed throttle switch positioning process is completed. Yours is sitting more rotated...maybe just pic angle? Don't forget feeler when setting it. Later Don

 

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Discussion Starter · #13 ·
I'm about to head out for the day, so I'll write more later. But I wanted to let you know that I just saw your TPS pic from a few posts back, and its looks like the the connector to the TPS is not on all the way. I'll post your pic below and then a second pic of a properly seated one.The yellow shows how far backed off it is. The red arrow is where the TPS tab should be seated but yours isn't there and is on the wrong side of the U retainer clip. Also, the pink bolt is generally near the middle of the adjustment slot when the closed throttle switch positioning process is completed. Yours is sitting more rotated...maybe just pic angle? Don't forget feeler when setting it. Later Don
You are correct that it is off-center. I just checked the plug and it seems fully seated. It has passed the retaining clip and only budges perhaps .5-1mm at most.
No time to check for codes today. Slept in and have a bunch of family stuff.

 

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Discussion Starter · #14 · (Edited)
So does moving the TPS sensor do anything while running? I barely heard a change when I was pulling on the harness connector. I unplugged it while running and there was no change. Shut it off, plugged it back in. Loosened the screws and straight up maxed it out side to side in the adjustment slots. ZERO change in idle. Set it back to its original position.

Went in the car and grounded pin1. Got codes:
14- never got this before. Probably because I unplugged it while running.
39- o2 sensor?? Never got this code before but i have both upstreams new in their box because i figured that might be my problem. Luckily the front is easy to test.
71- same TCS evap code i got before.

No code 62 this time.

Grounded pin6 but i got no blinking anything on the dash. My connector looks like an OBD2 and has a secondary connector with only 3 of approximately 12 pins in it. I'll get a picture of it tomorrow.

I'm resetting the ECU tonight and will report back on what codes come back. I'll try the "tap the TPS" trick tomorrow to see if it's something loose in there. Like i mentioned in another thread, sometimes the idle is butter smooth, but most of the time just feels a tiny bit off. No surging, no high 1300rpm. If anything, i feel a little low right at 700 with it just barely stuttering down to 670ish when warm.

How long does it take these older cars to register codes?
 

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So does moving the TPS sensor do anything while running? I barely heard a change when I was pulling on the harness connector. I unplugged it while running and there was no change. Shut it off, plugged it back in. Loosened the screws and straight up maxed it out side to side in the adjustment slots. ZERO change in idle. Set it back to its original position.

Went in the car and grounded pin1. Got codes:
14- never got this before. Probably because I unplugged it while running.
39- o2 sensor?? Never got this code before but i have both upstreams new in their box because i figured that might be my problem. Luckily the front is easy to test.
71- same TCS evap code i got before.

No code 62 this time.

Grounded pin6 but i got no blinking anything on the dash. My connector looks like an OBD2 and has a secondary connector with only 3 of approximately 12 pins in it. I'll get a picture of it tomorrow.

I'm resetting the ECU tonight and will report back on what codes come back. I'll try the "tap the TPS" trick tomorrow to see if it's something loose in there. Like i mentioned in another thread, sometimes the idle is butter smooth, but most of the time just feels a tiny bit off. No surging, no high 1300rpm. If anything, i feel a little low right at 700 with it just barely stuttering down to 670ish when warm.

How long does it take these older cars to register codes?
Do you have the factory service manual for your car.....94 Diamante LS DOHC NA with traction control and California emissions or just the Stealth/3000GT.? I'm not trying to be a PIA, just trying to help. But,as I said and showed you a pic, your connector and how it sits off the TPS is not what I'm,used to seeing. Doesn't sound like you did any testing or tried to set the base closed throttle position switch as required for normal ECU functioning. The computer simply ignored the non-sense readings from what you were doing and stayed in its fail-safe/default mode. When you disconnected the TPS connector, did you notice that the TPS unexpectedly only had 3 pins instead of 4? How many wires go into the connector, 3 or 4? Let me know those answers and I'll explain from there.
 

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Discussion Starter · #16 · (Edited)
I appreciate the responses. Really. I was just short on time. We don't have a garage, so I just went out and fiddled with it for a moment before pulling the codes. I run out of evening light very fast and my southern butt freezes under 60 degrees. After about 30 miles, the ECU seems to have settled back to its idle around 700. It was nice after the reset with the idle around 800 in gear. Seemed so much smoother.
Now at 50 miles since ECU reset. No codes yet. Just the continuous short blink meaning none present.
I plan to do a complete idle set and relearn this weekend with the manual. Also plan to drop the tranny pan and inspect/refill. Power steering flush, too. Hopefully the 3/8" fotting i found will suffice.

Next weekend or week after is plugs/wires and clean out the oil/carbon residue in intake manifold. I also want to investigate where that minute trace of oil is coming from on cylinder #1 plug. It wasn't burnt onto the tip, but it was up around the threads/gasket area.

Here are the relevant pages from my manual. According to the pictures, it should be 3 prongs on cars with TCL. Walked out to the car and confirmed it.
1
2
Empty
4
 
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