Subford handy punch down list as always.

RIKIL I doubt its the VSS/tone ring or its circuits but you'd have to test it if you had/have doubts.
I have a PSOM that jumps at speeds over 60, the PSOM is the fault.

I believe and have from the start (of this thread) you have two issues, only via some testing would you know for sure though.....well other than throw parts at the problem.

I think it's either this diode or it's gotta be the valve assembly. I do have one in my harness, be a pain to check that. I'd rather pay for the valve.

You'd rather replace a pricey valve rather then do couple tests first make sure its not the diode? Subford supplied the information required, only take a couple of minutes why not use it he being so kind as to provide it and all?

 

Maybe these diagrams will help:




/

 

I now have a way to use a multi-meter and record the results to a graph so I can capture the data. If I want to test the signal from the VSS, would I put one lead on VSSDIF+ and the other lead on VSSDIF-?

 

my truck did not like the aftermarket sensor I had to get one from ford

 

Same here. Bought one at my local parts store, and had to return it. The Motorcraft part fit better, anyway, and is working properly.

 

I have replaced these with an aftermarket sensor in the past, it seemed to be fine. I wonder if it's because my diff is just older. The jumping speeding started when a shop replaced it to fix my ABS light going on. And so far, that has worked to fix the ABS light.

 

I had a similar problem on my 95 that caused more problems on the E4OD. The bouncy speedometer caused the transmission to shift hard between gears. I cleaned the sensor on the axle and swapped it for a known working sensor. No change. I did some more research and found that the trans was controlled from a sensor in the speedometer and that the problem was in fact the speedo. I went to a boneyard and pulled a cluster from another truck, boom, fixed the problem totally and would't you know it the cluster was from a low milage truck, Knocked 100k off my odometer.

 

Third time seemed to be a charm...I went to Ford and got a VSS and now things are nice and smooth.

I did try to log it with a multi meter but had troubles with my laptop while logging, so I decided $40 for a new VSS was something to try.

 

Glad you found it!

 

I'm having the same issue with jumping speedometer. I've replaced the VSS(aftermarket), and have tried another speedometer cluster(which could be faulty also). I noticed when I had the RABS module unplugged, the speedometer worked fine. So does that mean the VSS is working correctly, and I possibly just have another speedometer cluster with a bad PSOM?

 

Guessing this is on your 1993 F250 so I will say not likely.
What you do when you unplug the RABS module is lower the load on the VSS signal train from the rear end.
In other words you either have a week VSS signal train (lower than normal out put from the sensor) or something is loading the signal.

This could be:
1. A week signal being generated from the sensor (too large of air gap or bad sensor or wrong sensor).
2. Extra loading from the RABS module (bad module).
3. Extra loading from the PSOM module (bad PSOM).

I would start by putting the sensor you took out back in as if it did not brake it more than likely OK. Was the junk stuck to it when you took it out?

Then look at the VSS signal train (with a scope or DVM at the hood hinge area drivers side) @ 30 MPH on jack stands.