I'm really confused. I started my 96 F-250 7.5L 145K put it in gear and it stalled. i barely got it home, running and stalling on the highway, shifting bad, and the speedometer was crazy jumping all over the place. i replaced the rear diff speed sensor, made the shifting way too soft and early, but the engine ran for a while and started stalling again, the speedometer still crazy. I switched the diff speed sensor on my other 96 F-350 7.5L with only 28K and didn't make any differences (F-250 keeps stalling and F-350 is just fine). i changed both speedometers and now the F-250 is up and working normal again, but the wierd part is the F-350 runs just fine, no engine stalling or change in the transmission shifting, but the speedometer is still jumping all over the place and bad i guess. I wonder why my F-350 can run using the speed sensor and speedometer from the F-250, but the F-250 won't run using it's original parts? At the very minimum, I need a new speedometer but the dealer says NOPE. i know the F-350 has a mass air flow sensor and the F-250 doesn't. Internet references say the speed sensor puts a signal to the speedometer, then goes to the computer. When I first unplugged the speed sensor cables, the engine revs up before slamming into second gear, which is the same exact behavior when i unplugged the speedometer, so i know the speed sensor is working from the differential to the computer, right?

 

To be more to the point the speed signal goes from the rear end to the PSOM and then to the Computer. The Speedometer does not output a signal at all, just moves the needle.
The F350 may need a new PSOM.
You can get a PSOM out of just about an van or truck from 1992 until they stopped using this system. But I have heard that there was an improvement to the PSOM in 1994. So you may want one from a 1994 or newer truck. But any of them should work. The Speedometer is just a voltmeter.

Any other problems us smart guys can help you with?

 

Subford, What is the PSOM, because my 96 F-250 7.5 is stalling (low idle) and speedo is jumpy (forgot to mention that in my thread)?

 

PSOM: Programmable Speedometer/Odometer Module.

The PSOM:




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Thanks for the diagrams and help, i really apprciate it. Is that something i can buy and put on the PSOM myself, instead of paying $150 for someone else to do it?

 

If you can take your Cluster out then it is very simple to swap the PSOM.
Note that the mileage is keep in the PSOM so you will now have the mileage of the truck you took it out of. Ford will not sell you a PSOM so you have to get one from a salvage yard and then you will have to buy the cluster from them to get it out.





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Note:
I have no idea how a PSOM would cause an engine to stall at any speed.
Jumping can be caused by bad rear end bearing or tone ring also.

 

whats weird is the F-350 runs just fine with the parts from the F-250. The F-350 has a mass air flow sensor and the F-250 doesn't, i think that is the only differences between the two trucks, both are 96's. The F-250 is running great now, shifting back to normal and everything. the shifting was acting a little weird for the last 6 months or so, some nice shifts, other hard shifts, the lockup clutch sometimes felt bad. But the problem was definately the PSOM.

 

I'm wondering if something you touched on in your last sentence could be the issue - if for some reason the lockup in the torque converter was on at low speeds, this could definitely cause the engine stall when you come to a stop. That was my first guess when the post mentioned stalling + speedometer problems - some issue with the vehicle speed sensor or associated circuitry.

 

the engine was cutting out bad on the highway, so would the lockup clutch cause the engine to stall while going at highway speeds, it seemed to stall more often as i went faster for some reason.

 

No it would not.
Also the speedometer would have to be saying that you are going above about 35 MPH while stopped for the clutch to be on while stopped.
But touching the brake would unlock the clutch anyway.