Overdrive, in and out

[Gio]

I have a 93 250 with auto trans, the trans will at times shift out of OD for no apparent reason, and some times will hardly go into OD at all. The trans works well otherwise. Could it posibly be a weak vacuum pump causeing the problem?

 

[RobertGray]

Did no one answer this? Seems like a throttle position sensor problem to me. Rob

 

[cerberusiam]

This one slipped thru the net.



OD problems can be either TPS or VSS, the speed sensor, grounds, or bad wiring. Its a process of elimination sometimes to find the problem.

 

[RobertGray]

If its the TPS the speedometer reads true but the truck drops out of overdrive, if its the speed sensor the speedometer dies and the truck then drops out of gear though it can be bad wiring to same. If the speedo flicks up intermittently, ie reads very high or goes to the top of the scale and the gear is unaffected then its bad dash wiring maybe. This happens to me, can anyone give me any clues as to where to start looking?

 

[Greenleaf]

The plug at No. 1 valve cover must be clean and tight.



The VSS should be replaced and the connector verified that it is clean and tight



The TPS should be replaced with a generic poteniometer



The above has eliminated any and all my problems.



Some have experienced a bad solenoid inside the trans, but 90% of the time it is the VSS and/or the TPS

 

[Gio]

Thanks

I wasn't sure where to start looking,

I thank all of you for your input.

I beleive I am going to change the TPS first and cross my fingers!

 

[ZedMikey]

Before you replace the TPS, verify it's adjustment. It is a quick check with a multimeter. When I bought my truck, it would drop out of OD at under light throttle. All it took was a quick adjustment of the TPS, and I was up and running smoothly again.

 

[ZedMikey]

A link for adjusting the TPS.

PDR Diesel Inc. The turbo diesel performance specialists! - 1st Gen TPS