I have a 92 1 ton and the over drive doesn't work. it only shifts the first 3 gears and doesn't shift in to over drive. I've replaced the computer in the truck the temp sensor on the trans and it still doesn't work. Does anybody know how to fix it?

 

Does the A/C and charging system work? A bad crank sensor or faulty wiring to it will kill all that stuff.

Have you adjusted the TPS? Check the sticky for info on doing that.

If that doesn't do it, install a temporary switch to ground the OD solenoid. It's the 2 wire plug on the trans, you want to ground the wire that's NOT blue while rolling at 45-50 mph. Make sure the blue wire has 12 volts when the key is on while you're laying under there. If the OD kicks in, then you know you have a control problem but the OD is mechanically OK.

 

the AC works and im pretty sure the charging system works. there was a temporary switch in it but i took it out cause it went 1-2-4 when it shifted and just completely skipped 3rd gear. ive adjusted the tps and it was set right. I have also gone through all of the wiring and tryed to test everything. weve tested the relay that was behind the glove box and that works.

 

I installed the switch in mine with the tps still plugged in and i just flip the switch to shift into overdrive when it is actin up. If you just leave the switch "on" it will do the 2-4 shift.

 

I had a question about testing the TPS voltage at the idle state and WOT state. When you test it what is the best way to test the voltage when the 3 pin connector is plugged in to the physical TPS sensor on top of the injection pump? Do you need to test the voltages when the throttle linkage is at idle and WOT with the 3 pin connector plugged in to the TPS or can you unplug the 3 pin connector and test the pins for the right voltage at the right throttle position? Because if not then you'd almost have to take the test pin of the multimeter and poke the wires right before the plastic connector. I basically have the same exact truck, a 1 ton 4x4 but it's a 93 (which I'm sure there is no difference) and have had the same problem with it not shifting into overdrive. I've been driving it with 3 gears only for the past 6,000 miles I've been using it to drive to work. No OD is a killer for fuel mileage also as the best I've seen from it is a little over 16 mpg. If I can fix it myself and avoid taking it to a reputable automatic transmission shop to have it looked at then I'll certainly do it. I just wanted to mainly see what is the best way to test the three wires at the joining point of the 3 pin plastic connector and TPS sensor (when in normal mode it's plugged in and you can't really test the pins if they are not accessible). Thanks for any advice.

Salvy

 

Salvy... first the best thing to do would be to replace the TPS with a potentiometer...Here is TuckerDee's write-up on this, very easy to do and very inexpensive:https://www.dieseltruckresource.com/...d.php?t=142641


BUT, testing a 93 one-ton( that is what I have) is best done this way:
Take a safety pin and WITH THE WIRING HARNESS CONNECTED TO THE TPS, slide it into the sheathing of the center wire right at the top of the connector. Connect the Neg probe of the voltmeter to the Neg battery post, and the POS probe to the safety pin.
Turn the key to the "run" position without starting the engine. You should measure the voltage "at rest" and at WOT this way.
At rest the reading should be between 0.6VDC and 1.2VDC, and it should smoothly increase by at least 2.25V as you move the thottle linkage from "idle" to WOT.
If it increases in jumps or sporadically, that indicates the TPS is bad or dirty,

Adjusting the TPS is done with the voltmeter connected and in the at rest position... there are "flats" on the shaft below the TPS which will accept a 10mm or 7/16th wrench. Turning the shaft clockwise will lower the voltage reading, CC will raise it. it is very sensitive, and you should make adjustments in very small increments.
Make note of your original readings as a reference BEFORE any adjustments.

I found adjusting the TPS did not solve the OD problems I was having with my 93, but installing a potentiometer did, and increased my mpg by almost 5, since i can "dial in" where I want OD to engage...

 

Chris, I thank you very much for your reply. I think this will help me to do this job all by myself and determine if I need to adjust it or replace this TPS with a potentiometer. If the latter occurs I'll make sure to give a look at the thread link you posted. I appreciate the help.

Salvy

 

i am having the same problem with the truck i just brought home tonight. i just want to get this straight. when testing the voltage if its jumpy while increasing to WOT then the TPS is either bad or dirty. if the voltage is not jumpy then a potentiometer could possibley be the solution.

my situation is a little different. my truck will shift into over drive when i am above 55-60 and will stay in. but when i am around 40-50 it will kick in and out of OD. sorry if i am hijacking your thread i just did not want to create another one.

 

Wire a 2-pole switch into your o/d solinoid which is on the drivers side right above the transmission oil pan. You splice into the green wire with the orange chaser and then you hook it to one pole on the switch, then you put a ground on the other pole and this will solve your problem for good. it only costs around $3 for the switch. The only drawback is that you have to flick the switch to go in and out of o/d which takes time to get used to but is easy to do.

I'll post pics of mine tomorro.

Hope this helps, Kyle

 

That scenario is typical of a TPS with a dead spot (usually worn in where the throttle sees most of its operating life). If cleaning it and correctly setting it doesn't correct things, then replacement is in order.

NOTE, when going the potentiometer route to substitute the TPS for overdrive operation, you lose the Cruse-Control function.

 

If the voltage is NOT jumpy or sporadic, but increases smoothly, then that is how it is SUPPOSED to behave.
What you are describing sounds like the voltage is set too high, causing the OD to delay engaging.
I would make note of the current reading at rest and try setting the TPS to a lower at rest voltage. Lower the voltage by increments of 0.2V and test drive it between each adjustment. IF the TPS is functioning properly, you should be able to correct the problem this way.
IIRC it should engage the OD between 35-40 mph, and shift into OD smoothly enough that you may not even notice it...
IF the voltage is jumpy and sporadic, then you can try cleaning the TPS, instructions for doing that are in the "stickey"...
If after attempting to adjust it and cleaning it, you still cant get it to set properly, then I would recommend replacing it with a POT.
Hope this helps!

 

Really?? I havent had any problems using Cruise since I installed the POT......works fine..

 

I thought I read that in the "Thread" about replacing the TPS. If such is not the case, I stand corrected.



In my mind, I wasn't sure how things would be effected regarding cruise. If there is absolutely no impact, then there's all the more reason for me to make the switch when my TPS buys the farm, if not sooner.

Thanks Chrisreyn.

 

well, all I can say is that I have installed the POT and my cruise still works... now sometimes if the tranny shifts OUT of OD, the cruise will shut off, but thats it..( like pushing the OD OFF button)...
I beleive the commnet you may have read was regarding the electrical brake light switch being maladjusted, causing the cruise to go off, that was mentioned in that thread..

 

thanks for the help, i will try adjusting it first. Also the previous owner said that it did it more often when it was wet or damp out if that makes a difference.