Hodge

I would imagine that this has been covered, and if so, just point me in the right direction of past posts. When I reach around 45 mph or so, and the trans has shifted into 4th/ lockup, it wants to jump/vibrate. I can take it out of overdrive, and it goes away. I had read somewhere (but can't find it), that this was a common problem, and if I remember correctly, you replace the PCM with a certain new one, have it programmed, and it will stop. Am I on the right track, and does anyone know the part number for the replacement PCM? Thanks in advance, and if this is a question that has been asked a million times, please forgive me in advance...

infidel

I think you're thinking of a TPS, not PCM.
Sounds like it's shifting into OD at too slow of a speed and lugging.
You might be able to adjust it out.
Instructions> http://dodgeram.org/tech/transmissio...TPS_adjust.htm

Replacement is easy if it can't be adjusted. Most autoparts have the TPS for around $150.
Or you could do as I do and push the OD off button until you're going over 55 and plan on staying that fast.

Crimedog

Infidel, I think he's talking about the reprogram that the dealer can supposedly do to delay the lockup until 50 mph. From what I've read the '94 pcms can't be reprogrammed, hence the need for a new pcm...? I haven't tried adjusting it out with the TPS, it would be nice if you could but mine locks up at 45 everytime unless I'm more than 2/3 into the throttle.

I am actually 70% done with a controller that will allow me to adjust the 4th gear engagement on the fly from 35 to 55 MPH, and adjust TCC lockup from 45 to 60 MPH, with the turn of two *****. I plan on doing a write-up on it when I get it done.

infidel

Like this?
https://www.dieseltruckresource.com/...d.php?t=142641

Crimedog

Similar, but not quite. I was going to do that, but the drawback is that you lose all the "automatic functions" of the automatic transmission. From what I gather, that just fools the PCM into thinking you are giving it a certain throttle, and constantly applying that throttle. It seems that you lose the automatic down-shifting ability, and it would keep your TCC locked until it hits the computer's threshold (something like 30 mph or around there?).

What I'm trying to do is have a controller that reads speed, trans temp, OD button, brake switch, and also senses if the throttle is just off idle. It uses this information and allows you to set the 4th gear engagement as well as TCC lockup (whether in OD or not). It lets you set it and forget it, and keeps the transmission automatic (just lets you control shift point and TCC lockup point).

I've got the programming about 70% done, once I ge that done it'll go in the truck and hopefully it works as simulated!

dguru

Hodge
Change the rear shocks.

The engine develops a harmonic with the rear at 45-46MPH (1075RPM) when the shocks are bad. It shakes the whole truck because the rear is flexing on the spring leafs. You might also have an injector that is not perfect making the problem worse(usually number 5). Traction bars would also stop the problem.

BTW if you get on the throttle a bit harder before or at that speed the problem will be less noticeable and you can cruise just above that speed. I feel your pain as I have a 94 as well.

Also those of you who want to add a pot and not lose the TPS. Hook some wires to the center wire on the TPS and the ground side(keep TPS connected). Run those inside to the dash. Get a 10K pot and a Diode. It is also a good idea to get a 220uf capacitor. Solder the striped end of the diode to the center post on the pot. Solder the center TPS wire to the free end on the diode. Solder the ground to one of the outside terminals on the pot. This allows you to adjust the TPS and thus lower the shift points and still have the TPS work. The diode is there to keep the voltage from getting too low at idle and throwing a code. The 220uf cap cleans up a bad TPS signal and gets soldered to the two wires from the TPS (+ pos side to the center TPS wire).

If you wanted to raise the shift points cut the ground wire going to the TPS. Connect wires to the wires you just cut apart and run them to a 5K pot inside without a diode. hook one wire to the center and the other to an outside terminal. Turning the pot to full resistance may throw a code so you may want to use a 1K pot instead of a 5K. The 220uf cap is still a good idea here too but connect it to ground and the center TPS wire. Be aware that this will change the shift points of both CL and OD.

Hodge

It's not the shocks. I know I saw a post on Dodgeforum.com, but can't find it. I will post a request on there. From what I read, it is a problem with the stock PCM, and the fix is an upgraded PCM and reprogram. Maybe I'm mistaken- it happens more than I like. But, I have a definite problem, which the truck has had for a long time- before and after the trans rebuild. Between 45 and 48, when in overdrive/TC lockup, the tail hops unless I disengage the overdrive. New shocks did not alleviate it. Has anybody else experienced this?
Thanks for all your help and input- this is a great forum.

dguru

The shocks helped me but did not get rid of the problem totally. Try adding a pot in the ground wire for the TPS. This will raise the TPS voltage and raise the shift points. Be aware that this will make it hold 3rd longer before it shifts to OD as well as raising the CL shift point.

Traction bars would eliminate the problem. If you ride next to a 94 at 46MPH you can see the rear end jerking front to back on the springs.

I still say an injector that is not spraying perfect will cause the problem. I know my number 5 is colder than the rest but it still idles ok. I have a new set but have not had time to install them. Plus they are stage 2s and the 94 has the 135 pump that may not push the stage 2s causing the problem to get worse. I am looking for delivery valves or a pump. I can let you know how that goes when it happens. I may just change #5 and see what happens.