Automatic shifting problems

[Berry]

Hello Everyone,

I have a 1991 D-250 with 75,000 miles and is completely stock. Yesterday while on the interstate traveling at about 70 mph it decides to start shifting in and out of overdrive. It did straighten up but now the shift point from third to OD has changed and it seems to shift out of OD at different points. Also seems like at times I can let off the accelerator pedal and it will shift into OD. Thanks!

 

[JHumphries]

It sounds like the dreaded Throttle Position Sensor.
Do a search for TPS.
Some members have replaced it with a resistor. I believe the TPS is a rather expensive piece.

 

[DVolk]

you might try some electricle cleaner and see if its full of crap ?, on the connections

 

[cerberusiam]

TPS or VSS, either or will cause the problem. Bad connections in old wiring will also contribute.

 

[Bob Beauchaine]

If it turns out to be the TPS you might consider the kit that replaces it - I believe Genos Garage has them for around $40. 00. I just helped my neighbor install one on his 91. 5 and he is quite happy with the result. It took him a bit to get it adjusted the way he wanted - adjustment can be down on the fly from inside the cab - but all is well now.



Bob

 

[Berry]

Thanks everyone, I'll get to work!

 

[HHhuntitall]

Don't forget to check the transmission fluid temperature sensor inline to the cooler. If unplugged, it'll hunt like that, too. Seems sometimes, they are only half-way unplugged, or working intermittently, they'll perform the way you're describing. Not saying it's not the TPS, but I've seen those get replaced and the transmission still not shift right.....