I'm trying to diagnose an issue on my 97 Ram 1500, 5.9L. Mods are 4.56 gears, hemifever tune, and CAI. Plenum has been fixed with an aluminum pan.

I have approximately 116,000 miles and the transmission still shifts fine and does not slip. The issue I have may be with the torque converter.

When driving I'm overdrive when I start to go up a big hill, the torque converter will not unlock unless I go at least
about 3/4 throttle. The truck will slow down going up a large hill and get as low as 40 or 45 mph and it still won't unlock or shift down unless I push the accelerator almost to the floor. When I am going slower and it finally unlocks, the truck actually shifts down to 2nd gear because it is going so slow.

The throttle valve cable is adjusted correctly but that shouldn't affect OD or TC unlock because it is controlled by the PCM. What I am trying to figure out is what tells the PCM to unlock the torque converter and/or downshift out of OD. I know the TPS most likely controls this but are there any other sensors that come into play?

When I get a chance, I am going to start diagnosing by checking to see if the PCM is giving the signal to unlock the converter. If it is giving the signal to unlock, then it could be an issue with the converter itself or the solenoid in the transmission. I believe there is a valve that is activated by the senoid in the transmission that locks the converter that could be an issue also.

If anybody knows what signals the PCM to unlock the TC and/or downshift from OD that would be a great help. Also what happens in the tranismission once it receives the command to unlock or downshift out of OD?

 

PCM just controls the grounds for the O/D, and TCC solenoids. The solenoids just route fluid to the correct spots, for hydraulic engagement of tcc, and/or o/d. The PCM should drop out of o/d, and/or unlock tcc at some specific load value/engine rpm/vehicle speed. I know when I am on cruise, it is REALLY reluctant to do either, and slowing way down up a hill is pretty much a given, unless I step on the gas.

It's all in the programming. Hemifever should be able to tell you just what conditions should prompt the trans to downshift, but, large throttle openings is most certainly one of them... You shouldn't have to have the pedal most of the way to the floor, before anything happens.

If you can read live data, see what your TPS value is at idle, and again, at WOT. Testing with an analog multimeter is sometimes better... as you get a much better idea of the stability of the signal from the TPS......

 

This might help...

https://dodgeforum.com/forum/2nd-gen...tcc-locks.html

 

Thanks for the post about the LED. I actually hooked up an LED today for the exact same reason.

What I found is the the TC locks and unlocks when the PCM tells it to in OD. When I have OD locked out using the button on the dash and the transmission is in third gear, the TC locks sometimes but other times it won't lock. I think this is a problem with the TC. I will most likely replace it since the transmission still seems solid.

As far as the TC not unlocking going up a big hill in OD until I am 3/4 throttle or more must be either the way the PCM is programmed or a sensor is giving the PCM bad info.

Best I can tell, the TPS is working normally. Before I made this original post, I had "adjusted" the TPS to 1.0 volt at cloed throttle and reset the PCM. This adjustment had no affect on the TC unlock. Also using the torque app, it shows the TPS as 18% when closed and 76.9% when wide open. HeyYou had asked for the TPS values.

Now i need to figure out what other sensors are used by the PCM to make the decision to unlock the PCM. HeyYou said the load on the engine might be a part of the PCM deciding to unlock the TC. I wonder if the 4.56 gears cause the PCM to see a lower load on the engine so it doesn't want to unlock the TC or downshift until i really get on the gas hard? How does the PCM dtermine load? I'm guessing it takes input from several sensors to determine the load. If lone sensor is out of range it could throw this determination out of whack.

I'm also going to email Hemifever to see if he is able to adjust these parameters.

If there is any other advise or anything else to check I'd love to hear it.

 

I was just reading the transmission diagnosis sticky and under the section explaining how to diagnose downshifting problems it lists possible issues with the 3-4 shift valve and 3-4 timing valve.

I don't know that much about transmissions but i wonder how these valves work or if they could be causing me an issue. Especially the timing valve.

 

What did the LED tell you, with the OD locked out? Is the PCM turning on the LED, telling the TC to lock up and it just doesn't feel like it is? Or is the PCM not even trying to lock up?

 

With OD locked out the PCM tells the TC to lock up in third gear but more times then not it didn't lock up. It did lock up a few times after commanded to but I couldn't figure out what made it lock up those few times.

In OD, it locked and unlocked consistently when the PCM commanded it to do so.

 

It's a mystery why it does it one way and intermittent the other, but it may be worth changing out your governor pressure sensor and solenoid. Maybe your OD and lock up solenoids too.

 

All the same circuits (electrical, and hydraulic) are used to lock/unlock the TC, regardless of O/D enabled or not..... I wonder if it is just harder to notice in third, than it is in O/D? (mine sure is.....)

 

Mine is too. I just assumed (yeah, yeah, I know!) that they were paying very close attention.

Heck, if it weren't for my idiot light, I would really not notice it.