Hi All,

I've got a bit of an odd issue and haven't seen any threads that go over my exact problem either on here or anywhere else for that mater.

First off the vehicle in question is my 94 F250 7.5L EFI with E40D trans. I purchased it with quite a bit of mileage on it (220K) but it was a steal so I thought why not? I've come to learn that with these early 90's vehicles it's not the mechanical bits you need to worry about but the electronics. Basically, a few weeks after I bought it, the speedo started doing something odd. At around 65mph, it would swing wildly and sweep the gauge from 0 to 80. A bit of digging online I was concerned that I might have a PSOM issue. So I refurbished myself. The issue didn't go away.

I drove it like that for a while and continued to look into potential issues. I came up with ABS, VSS, and worst case scenario: tone ring. Over last weekend I decided to just replace the ABS control module and VSS as they were both easily accessible and no more than $125.

It worked for half a day. I was able to get the truck up to freeway speeds without any wildly out of control speedometer but I did notice the gauge was a little jittery, even at low speeds. Then it just died. Gauge was stuck at 0mph and the transmission would slam out of 1st at 3,500RPM. Basically I had to limp home.

About half way home I got fed up, pulled over and disconnected the ABS controller. It was like a brand new truck. No speedometer issues, not even the aforementioned jitter.

I've been driving it like that for 3 days now without and ABS warning light or anything. This brings me to my main questions. How does the ABS controller communicate with the PSOM? Could my symptoms indicate a larger issue than just a bad ABS controller? And lastly, is there any harm in driving without the ABS controller connected?

Thank you for the help in advance.

 

Sounds like a week VSS signal from the rear end.

 

That was my thought, but after disconnecting the ABS control module, all the problems are gone and the speedo is more stable than I've ever seen it. It doesn't make any sense to me and it's driving me nuts.

 

If the signal from the rear end is weak from the rear end it might be strong enough for one module to work OK. Then when you put two on the signal only one module may work or neither module may not work.
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