What's up fellas,,,
I'm currently working on a 94 F150 ( 300cid , Auto w/o.d. ) for a friend. Itermittantly his speedo quits working, odometer goes blank and it slams between shifts. This might happen once every few months.

Seems to me that it must be a speed sence issue or maybe the ecm.... Any Ideas ??? Any help would be greatly appreciated !!!

 

It would be the VSS or PSOM or the wiring between them.

 

weird thing.... the odometer and interior light share the same fuse... I know this cause I was doing interior work so i pulled the 15 amp interior lamp fuse so as to not drain the battery...later when I went to drive the truck the tranny was acting up and overdrive was flashing it took me a few minutes but I realized the odometer wasnt working so I then remembered and put the fuse back...then everything was fine...

I dont know if that info helps at all...but it was interesting that a loss of the interior lamp circuit power effected the transmission...

 

I'll check that fuse, maybe it's losing contact from time to time....Thanks

Please excuse my ignorance,, What is the "VSS" & "PSOM" ?

 

VSS vehicle speed sensor located on top of the rear end pumpkin
PSOM programmable speedometer odometer? module
go hear and it will explain in great detail that I cannot begin to type out
www.fordfuelinjection.com
the computer depends on the speedometer and all related
components to run the engine and tranny properly

 

Thanks,,,, I changed what I thought was the VSS, it was located on top of the rear diff. i thought that would take care of the problem but it didn't. The book actually calls that a RABS sensor ??? something to do with the ABS.

I have no idea where to find the PSOM, I had the trans out to change the torque conv and didn't see anything that looked like a speed sensor.

 

They use RABS and VSS interchangeable sometimes but not always.
The PSOM is behind the cluster, here is a photo.

/

 

Thanks Subford,,,, You reckon I need to go ahead and change that next ???
Are they available aftermarket or dealer item only ?
Is the PSOM that entire printed circuit board ?
Are they serviceable ?
The check engine light isn't on, Would the intermittant problem log a code on the ecm ?

 

No, make sure your wiring is OK and the VSS sensor is clean and OK before you go after the PSOM.
Salvage yard only, A Ford dealer will replace it but you will not like the BILL.
YES in the photo above.
No except at a Ford dealer.
Most of the time it will not.

 

I guess I'll break out the schematic , check the harness and if all looks well there I'll go ahead and pull one from another truck. Thanks again for all of your help.

 

Just remove the PSOM from the salvage yard/ebay cluster and put it in yours. Try to get one from 1994-1996 if you can but I think ones all the way back to 1992 will work from a truck, Bronco or van.
Note that a PSOM is where the total mileage and tire size of the truck is keep. You will get the mileage of the truck/van you remove it from and you will have to reset your tire size in it, this can be done up to four times for the life of the PSOM.
This is not legal but it is what most of the posters do.

 

Check the VSS...if you put a new one in and that still doesnt work check the wiring....i had the same problem and replaced the vss and it still didnt work...had it to numerous shops and they couldnt find it....so after getting a ticket bc i had no speedo i was messin with it one day and pulled on the vss wiring one by one and the one wire was corroded in two about 6 inches up in the loom