just tried two working computers in my 3/4 auto. truck will not shift out of overdrive while travelling slow speeds in town. so i have bypassed withe a switch to do so. any ideas what mite be the culprit? both computers charged , air cond works, wait to start lite etc and grid works. so i dont really think it is computer related?

 

Adjustment is needed at the TPS or TV cable is out of spec if 1-3 don't shift all to well. if they shift fine then the TPS needs fine tuning. I ended up using a switch for a year and now my O/D clutch pack fried recently so I have my truck prepped and ready for a getrag to go in.

 

It's almost never the computer with OD issues. Do a search, there's about a hundred threads with various OD troubleshooting and solutions. Personally mine is on a footswitch like the old headlights and it lights up the "od off" button to indicate status.

 

ya i believe mite be a TPS issue? i like the footswitch idea i just use a toggle now thanks

 

Mine was a TPS, if you've got a multimeter you can test it, they usually get a "flat spot" and then you don't get a proper reading to the computer, I thought about altering the overall resistance to trick it into operating in a different range of the varistor, but I like simple. PLUS if anyone else drives my truck, they can't go over 55

 

Since it doesn't shift out, I'd try adjusting the cable first, pretty simple anyway.

If it's the TPS it seems like it would be hunting and going in and out of OD all the time right?

 

i had another tps new one tried it but that did not seem to cure the problem

 

Just to clarify, you can't just throw it in you need to adjust it when installed it doesn't matter where you buy it from 99% of the time it will not be adjusted properly.

 

so what you are saying they may not work at all at any speeds till they are adjusted?

 

The Tps controls the signal out of and into O/D when the factory dash O/D switch is on.

 

If you turn the factory dash switch off then the tps has no say in things because the signal wire grounds the solenoid so it won't receive 12 volts to turn on O/D. The tps cannot Override that.

 

Yeah there's also a temp sensor in the mix. Can't remember if the CPS is in the equation too, but youd lose charging and ac. It can prevent OD if it doesn't think the trans is up to temp or a wire is broken. The book has a procedure for setting the TPS with a multimeter. I forget the voltage range, but I think 5 volt based iirc.
Internally youve got the solenoid spring and electromagnetic solenoid in the valve body, my solenoid went south. The unit itself is pretty stout once it's spaced and assembled correctly.