Revisiting this project van of mine. I've been having intermittent issues with the speedometer and odometer. Removed the PSOM today and cleaned the contacts (both clip and PSOM side) and reinstalled.

I also replaced the sensor on top of the rear differential. Now, my speedometer AND odometer work perfectly... but only at speeds between 10mph and 35mph . At speeds outside of that range, the speedometer drops all the way back down to 0mph and the odometer stops clocking. (I also found out today that I can get this exact same result with the VSS totally unplugged from the harness. Is that not where speed is read and sent to the computer??)

With ignition turned to RUN, I get a 1.3V multimeter reading out of the harness at the rear differential, and my repair manual says I should be getting 10V. Can anyone else confirm 10V out of the harness here?

Now, I've been reading that speedo/odo problems can be cured by just replacing the cluster altogether. I found a compatible cluster at a Pick N Pull locally, and at $45, I'm planning to go grab it tomorrow and see if that fixes it.

But, it occurred to me today... would the so called voltage shortage I'm experiencing be due to a faulty PSOM, or a faulty PCM?

 

Pulled the $45 cluster from a 98 E250 4.2L Superduty at a pick n pull today. Planning to install tonight or tomorrow.

 

Back when I had a 95 E150, it's speedo went out and I ended up paying the local Dealer to change the whole speedo unit for $800 to fix it. I read somewhere back then that changing tire sizes too many times will kill the PSOM with 4 wheel antilock brakes. Made sense to me as that's exactly what I had done before it went south.

 

Well I'm not sure I understand exactly how this speed circuit works, but I got lucky and replacing the cluster fixed it. Speedo/odo have been working perfectly for ~700 miles since last Wednesday.

I am still getting the 1.36V reading out of the harness at the rear diff.

 

when i bought my van the speedo/odo was not working which ultimately caused transmission shifting issues and hence i got the van for 300 bucks.....

after some guidance from my master mechanic friend and his recommendation to take the cluster out and send it to a "module re-builder" locally, ended up being some components on the circuit board being out of spec after 22 years. and 140 bucks later i had a working speedo/odo and a properly shifting transmission.

yours may be repairable yet?