Archived Help! TC not locking up at all on '94

[Sojourner]

About 7 or 8 months ago (< 10K miles) the TPS was replaced on my '94 CTD due to the typical locked/unlocked action at highway speeds. I am uncertain if this is related, but prior to replacing the TPS, once in a while the torque converter would unlock at highway speeds, illuminating the orange LED on the 'O/D UNLOCK' button. I would simply cycle the button and it would go back into lockup. After replacing the TPS it would still do this same thing once in a while.



I went out of town for five days, parking the truck at the airport. It acted fine prior to parking it for five days, then when I drove home the TC would not lockup. I took it to the dealer, and at first they told me the bushings on the linkage were worn out and they replaced those. I also had them install a new throttle cable at the same time (200K miles on truck). Now they tell me they can't get the voltage from the TPS down to where it should be and they are saying that the next thing 'we need to try' is replace ALL the linkage as well as the 8 month old TPS (they tell me the TPS has 'worn into' the old linkage and will not work with the new). This amounts to about $800 in parts even with my discount. Then the tech tells me, "There is no guarantee this will fix the problem, it could be in the transmission. " At the moment the service mgr. who is a good friend is out at a business conference and I am without his counsel.



Help! I can really stand some direction here. All input appreciated. TIA!

 

[Joe G.]

RUN FROM THAT DEALER!!! Lockup is controlled by a solenoid on the VB. It's not voltage that is necessary to cause a lockup. It's ground. The voltage should be there anytime the ignition is on. If your OD will work, but not the TCC lockup then you are not getting the ground to the solenoid or the solenoid is bad. Remember, OD and TCC lockup use a different solenoid in the 47RH transmission. Linkage has nothing to do with if the TCC will lockup. Linkage may affect pressure, but you should still be able to cause it to lockup. You can test this yourself. Get the instructions on how to wire a manual lockup switch (AKA mystery switch) on the 12 valve engine forum at the top. Rig a wire to the wire that the switch grounds in that circuit. Get the truck up to speed on the highway and ground the wire. It should lockup. If not, lift your foot and press down again. It should lockup. Sometimes a 47RH is kind of finicky about locking up so you have to mess with the throttle. If that works then you want to check the TPS to see if it is making the right voltage on the signal wire. Search the 12 valve engine forum for TPS and Howard Durand's discussion of how it should work. In the mean time, until you have better information, keep the truck away from that dealer.

 

[Sojourner]

Thanx a bunch for the info, Joe!



I will try to troubleshoot it via the means you suggested tomorrow.



I talked to someone today who said it could be one of three things:



1) a noisy electrical signal from the alternator;

2) TPS voltage isn't right;

3) TC lockup solenoid.



It 'appears' to be going into O/D, because if I hit the O/D OFF button at highway speed the engine RPM will instantly run up, and when the O/D OFF button is not illuminated the engine speed will vary quite a bit at highway speed when fluctuating the throttle (whereas it will not when the TC is locking up as it normally should).



What else other than the linkage (?!) would cause the TPS voltage to be thrown off??? (provided the problem is not a noisy signal from the alternator nor the TC lockup solenoid)

 

[Joe G.]

The TPS could very well be dirty. If so you can clean it. Take a look at this thread for some good info: https://www.turbodieselregister.com/forums/showthread.php?t=130979

 

[JFaughn]

What about your cruse control ? I had a simler probulm , the dealer [ owner before me ] put in a TQ conv. still had prob. I noiticed that the brake sw. needed adjustment, but there is none on mine so I hot gluded a small washer on the foot of the brake sw. and now my lockup and cruse work just fine 4mths later.

 

[Sojourner]

Okay, here's the latest: Joe, despite your suggestion that I 'run from that dealer' I have hung in there because I have a five year relationship with the service mgr and he has saved me several hundred dollars on my '01 CTD (I won't go into the details, but it has been substantial and he has gone above and beyond). He's a good friend and I trust him to do exactly what I tell him that I want.



Anyway, he warrantied the TPS and we still couldn't get the voltage down to one volt. Next we replaced the throttle cable and linkage, mostly because the '94 has 200K miles of 'in town' driving, plus I am constantly in and out of the throttle (this is not the first instance of me wearing out throttle linkage on a hi-mile, in-town driven truck) - a good analogy in my mind is trying to align a sloppy front end, drive it off the rack and around the block, then when it's rechecked the alignment is off again. Same thing with getting rid of the sloppy throttle linkage in order to get consistent results.



So now we still can't get the one volt consistently - blip the throttle and it won't return to one volt, it comes out to 1. 5 to 1. 8 volt, then eventually settles down. There is no lockup occurring at all on during the road test. The service mgr suspects the aforementioned highly intermittent problem of the transmission dropping out of O/D at highway speeds on its own is somehow related to this, however there has been no recent instance of this happening in the past 4 - 6 weeks as well as there not having been any increase in the frequency of the dropping out of O/D at highway speeds. in the 30 months I have owned the truck, I doubt that has happened more than 18 - 20 times so it never really concerned me (I had thought it had something to do with a bad TPS, but it continued after the TPS was replaced).



As for the brake switch issue, coincidentally the brake light switch started hanging up and leaving the brake lights on in conjunction with the failure to lockup the TC (the brake lite switch was replaced about 8 months ago as well) and we are replacing that next. Could the brake light switch cause this kind of problem???



Any ideas???



TIA!

 

[Joe G.]

It could be the brake light switch. The high voltage for the TPS makes me think you have a bad ground somewhere. You should have 5 volts on one of the TPS terminals, ground on another, and varying voltage on the other. At idle throttle my TPS had . 5 volts. So do most of the '94 and '95 I have had anything to do with. The manual says 1 volt, but I have never been able to get that voltage with a stock TPS.



I had one experience with the local Dodge dealer that you might find interesting. A friend works there in the parts department. He was having a problem with his '97 and none of the mechanics could figure it out. From his description I told him it sounded like an AFC problem. "What's an AFC?" I told him about he. Then he dragged me back to the shop so talk to the mechanics. That's what it was. These '94 and '95 trucks are mechanical monsters, the rest of the stuff the dealer mechanics work on are computer scooters.

 

[Joe G.]

After thinking about this for a little while I'm pretty sure the high voltage on the TPS is what is causeing the no OD and no lockup. If I remember correctly, Howard experimented with high voltages on his '94 TPS and found that it would not shift to OD or lockup above a certain initial voltage. It appears that the PCM senses WOT so is in a "kick down" condition.



I don't think sloppy linkage can do what you are reporting. Mine was pretty sloppy before it was replaced by a recall. No affect on transmission operation. Most of the complaints about 47RH OD and lockup are that those things happen at too low a speed.

 

[Sojourner]

Thanx again for the info, Joe.



We are going to go at it again tomorrow after I pass on your info to the service mgr, after which I will post the results.

 

[Sojourner]

We really didn't make any progress today, as they were short 'technicians' (notice how they are all 'technicians' who throw parts at the problem and not actually 'mechanics' anymore) and I had to pick up the truck to go put some new tires on it.



What I did notice when I drove it home was that this new linkage is noticably much stiffer than what it was before replacement. Also, when I initially took the truck in last saturday the truck was actually going into O/D, it was just that the TC was not locking up. Now the transmission won't go into O/D at all. Apparently they're in the ballpark, just going the wrong way.



The TPS voltage has been varying from 1. 008 volt to 1. 5 - 1. 8, all the way up to 2. 1 volt. They have told me that have checked the ground, but it is going to be re-checked by someone else next week.



We are in agreement that until we straighten out the TPS voltage issue and get that consistent we should not consider the transmission to be the source of the problem.



The questions I have right now: Is the PCM causing this TPS voltage problem? Could there be a wiring problem somewhere else, like in the vicinity of the transmission?



I have been getting an intermittent WAIT TO START lamp illumination (flashing) from time to time, any time the truck is in operation, which was a hardly noticeable problem a couple of years ago (supposedly addressed by the dealer about two years ago, at which point it seemed to quit, then re-occurred periodically a couple of months later), but now it is a very common occurrence. When the WAIT TO START light flashes, it flashes in a very consistent pattern, as though it were some sort of trouble signal/code. Could this be a sign of a PCM problem?



What should we look at next? This is crazy!

 

[Joe G.]

Until you get the TPS voltage to behave then messing with anything else is a waste of time. It could very well be a bad PCM. I don't know how to check that. There still may be a bad ground somewhere.

 

[Sojourner]

I agree, I don't think they have exhausted the trouble-shooting of any ground problem. Also, since the 'technician' was the one who made the recommedation to replace the linkage and we are still exactly at the point where we started, I think they bought me some linkage.



The latest update: I took the truck to the tire shop today and got a new set of tires. I took the opportunity to spend some time making some observations as to how the transmission is operating. I was mistaken about it not going into O/D (the tech was claiming it wasn't going into O/D, but apparently he didn't take to 62 MPH), it does, just not how it should/typically has in the past. When accelerating, the transmission shifts into O/D at 61-62 MPH regardless of throttle position. When decelerating, the transmission drops out of O/D at ~58 MPH, regardless of throttle position. These speeds are consistent, whereas before it would be variable as to when the transmission went into O/D depending upon throttle position (often going into O/D under 45 MPH under light throttle pressure), and it would never drop out of O/D noticably upon deceleration.



So that is where it stands now. Thanx in advance for any additional ideas/input.

 

[Joe G.]

I think I would especially make sure the PCM ground was good. The fact that the throttle position has little or nothing to do with your OD shift point I would suspect the PCM. I don't like to advise trying it and see if it solves the problem trouble shooting, but that may be what you have to do. I don't know how to trouble shoot a PCM so trying a good one is all you can do to check it.

 

[Sojourner]

They are now telling me that they've eliminated everything but the PCM. :{

 

[Sojourner]

Anyone in central Texas got a '94 PCM for an AT truck that I can borrow for a trouble-shooting episode??? Please?



The re-man unit is $492 +/- $100.

 

[Sojourner]

They finally find the problem causing the TCC not to lockup - the bracket that the TPS mounts to somehow got 'bent' (?) which caused pressure on the side of the TPS, which in turn caused inference in the mechanical action of the TPS. I was told they mounted a washer between the bracket and the new TPS (replaced a 2nd time under warranty). Both the 8 month old TPS and the recently installed TPS showed deformations in the plastic bodies as a result of this out of shape bracket. (I haven't personally seen the parts yet, this is what was described to me over the phone). The new linkage and cable were N/C because of the missed diagnois.



Thanx for everyone's input and suggestions.