I just got the factory manual on CD from Geno's garage so if schematics would help you I could send them to you. Like I said before I gave up on trying to diagnose and fix the pcm system and did the bypass thing. If the external regulator has power to one lead lead and grounding the other makes it charge the regulator has to be bad. Some auto parts stores can test the regulator to make sure though.

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If you want to automate the OD shift you can add an adjustable normally open hobbs switch to one of the ports on the tranny and set it to whatever speed you want it to engage, That is what I did with ours. Then the toggle switch can be used to disable it when you don't want it to work

 

Does your OD work normally? If not, then the PCM is not getting voltage. Give me a call and I'll walk you through it. Went through it on my 91.5.

 

The OD wasn't working when I got the truck, replaced the speed sensor and took the TPS loose to test, it still wouldn't shift. So I wired a toggle switch to the ground side of the solenoid. When I want OD, I flip the switch, allows me to shift it when I want based on load, how hard I'm accelerating, or if I'm cruising and want to grab it early. I will be down where I can put my hands on the truck on Sunday, is it ok to call then? I really appreciate all the help. As for the external regulator being bad, I can have them try and test this one as well. Drives ya crazy that you go through all these parts and replace really expensive ones to find out they weren't the problem at all. Oh well, guess I have some spares now.

 

Updates??

 

trans temp switch in the 1st gen diesels was a huge culprit in the no OD situation
93 and older use a switch and 94 and newer use a sensor (both plug in and thread in and look identical) make sure you get the right one

 

No real updates, haven't had time to work on it, trying to get moved currently, but did drive it from Orlando to Jacksonville FL, about a 2 hour trip without any problems, only had to use the headlights at the very end of the trip and had enough battery for that chore. But as soon as I figure out anything or have them try and test the voltage regulator, I will update the thread. Thanks again for the help. As for the temp switch/sensor deal, I'm wondering why they use so many sensors that are known to go bad for something like OD. I guess they want to really know what's going on everywhere to get the thing shifting right. As before though, the toggle switch is still working wonders on the OD problem

 

A beer bets your PCM is not getting voltage from the battery to turn it on, therfore, the PCM can not tell the voltage regulator to take over control of the field. Give me a call and I can go over the PCM pin out and we'll see if your getting voltage where you need.

After I got voltage to my PCM, we found that the PCM was toast, giving 5v to the TPS and provind 5v on the sensor pin, thus the transmission would never go into OD on its own. I did the switch thing for a bit and fixed it with a 5 speed. . . . .

 

Not too particularly worried about the OD right now, but if the no voltage to the PCM is causing all these problems, that will be what I need to fix. Still haven't had a chance to go through and try some of the suggestions offered yet, but I'll be glad to give you that beer if that fixes the trouble, I should have some time Friday to work on it, off of work that day, so I'll give you a ring for sure. Thanks again for all the help guys.

 

Updates please.

 

Please update.