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Discussion Starter #1
Yup. My OD is starting to act up. It use to be weird when I first got the truck (winter). Now (starting to warm up) I will be cruising about 70mph on the highway and itll downshift randomly then i have to let off to get it back into OD. Itll do this about 10 times on a 20 mile trip (all highway).

It seems like its getting worse... i dont know if its temperature related or not because its starting to warm up and it seems to be getting worse and worse. What should I do to start troubleshooting/fixing this issue? Im sure its not good for the motor/tranny/fuel milage.... so i want to get this fixed. Thanks for all the help in advance.
 

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I had the same problem. If you look under the hood you should see a small black box that is connected to your throttle linkage. This controls the electronic overdrive. That is where I found the problem. Good luck.
 

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Discussion Starter #3
Did you replace it? Or was something loose and/or dirty? What was your solution?
 

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I used two wires, one switch, the overdrive is full manual now, I have no problems.

 

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The TPS is the little black box on top of the injectin pump. Unplug the 3 wire harness. Look real close inside the plug. You will see there are two very small tabs in each socket. Take a very small screw driver and bend those tabs gentley outward. Then apply some dieletric grease and reinstall the plug. Do a long test drive and see if the problem goes away.

If it doesn't I walk you threw checking the TPS setting. You will need a volt meter fot that.

What are the road conditions when it drops out of OD. I.E. is it droping at the same spots every time or is it random in its action.
 

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Discussion Starter #6 (Edited)
What are the road conditions when it drops out of OD. I.E. is it droping at the same spots every time or is it random in its action
Its very random, it doesnt seem to have anything to do with driving conditions at all.

I was wondering if you could use a switch to control your OD the other day... Can you let me know how to do it?

In the mean time ill check the plug and bend the tabs to see if thatll help..

By the way what regulates the voltage levels in the electrical system? Do these trucks have BCM (body control modules)? I think whatever controls voltage is going south =/
My voltage levels are all over the place (mostly high), it also flutters alot... and i know its not just the gauge because i can see the lights (dash, headlights, etc) dimming and getting lighter.

I dont know if my voltage levels would have something to do with OD or not.
 

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On the transmission, there are three wittle electrical plugs. One is the start-neutral-safety switch. That one's horizontal. On the tailshaft, there's a speedo plug. And then, up near the front of the transmission near the shift linkage, is a plug with two wires coming out of it that points straight up. That plug controls overdrive.

First of all, don't break or loose that plug. There are three of them in the country, and none of them are for sale.

One of those wires is a ground, one is a positive. When you give the positive wire 12 volts, the transmission goes into 3rd high. Without the positive 12 volts, it will only go up to third.

So you trace back the wires, put the hot wire on a permanent hot, then put a switch on either the hot or the ground.

I don't think that polarity matters; I got lucky and mine worked the first way I wired it, so Murphy's law states that polarity probably doesn't matter.

Voltage on the later trucks, from what I hear, is regulated by the ECM on the firewall. When that goes bad it's north of over $100. However, the earlier trucks use a $25 external voltage regulator that hangs on the firewall, and that can be retrofitted onto yours.
FAQ

Or if you're more creative, I found this one.
NipponDenso Alternator Regulator - Dodge Diesel - Diesel Truck Resource Forums
 

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Discussion Starter #8
Does anyone have a picture of this ECM or info on where it is located on the firewall?
 

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If it's in the same place as the black box on the early trucks...

Under the master cylinder, over towards the driver's side.
 

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On your 92 the PCM is located behind the battery.

I have had problems with the plug on the PCM. The terminals are round and the female sockets like to go egg shaped. I took a small screw driver and reshaped them.
 

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I, brother, and friends have experienced the TPS problems over the years. I came up with a fix about 6 years ago that has worked flawlessly for us. I squirted wd40 into the fitting where the plug fits into the TPS on top of the injection pump. I removed the plug and liberally flushed it. I've redone it a couple of times over the years with the same result. After several miles of driving - problem gone. It sounds hokey, but it works. I've wondered for years how many of those things were replaced - needlessly - at $200-400.00.
 
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