Hey All. Is there any truth in a PCM needing to relearn shift points after being swapped? I have a 94 F250 5.8 E40D. I put in a new PCM( remanufactured FS1). I was not able to move the truck before swapping the pcm. It misfired like crazy with the auto OD light flashing and truck would not move in any gear because of the misfire.
After swapping the PCM i was able to drive the truck again and motor runs just fine. The issue i am having is when it shifts largely from 1-2. its a little hard. I also still have no speedometer and no odometer. I swapped the VSS no change. Fuses are good and the dome light and 3rd brake light works fine.
I read many of the threads and still chasing the speedo issue but I am curious if the computer is still learning shift points. I have driven about 120 miles since the PCM was installed. Any help would be greatly appreciated.

 

You have to resolve your odo/speedometer issue before the shifting will correct itself. Is the odometer display blank with the key in Run position?

 

The odo display is not blank, it shows 160 xxxx but does not move. The speedo does not jump shake rattle or roll. I suppose i could have gotten a dead VSS from NAPA? Thinking about trying that again just to rule that out.

 

Replacement sensor quality is hit and miss these days but chances are you have a wiring problem under the truck somewhere or an issue with the PSOM in the gauge cluster, it's the part that converts the signal from the VSS and drives the speedo and ODO.

 

Would that also cause the slight hard shift? What is involved in swapping the PSOM or the whole cluster?

 

Yes that would cause hard shifts, that is exactly what the PCM is programed to do in the event it loses it's speed input signal. The PSOM is mounted on the back of the cluster so it has to be removed to access it.

 

There are several threads with info for how to verify the VSS signal is getting to the PSOM. In the meantime you could remove the gauge cluster then inspect the PSOM for signs of broken or loose components.

 

Not in a 1994. Learning didn't start at Ford until 1999, and then only certain vehicles.

 

I think you said that you replaced the rear end (3rd member) in another Thread.
If so you may have a bad tone ring.

 

Hoping it is not the Tone Ring.
I replaced the VSS early on with a Napa part. When it made no change i put the old one back in. I spoke to someone today from clusterfix.com. They repair your PSOM. I was told that if i have no speedometer and a blank odo it could be the Psom. However i was also told that if I can see my odometer but it does not count then it points to the vss or wiring and more than likely not the PSOM. I am going to swap in a MotorCraft VSS first at their recommendation and also because sometimes you do get a bum electronic part. Wishful thinking. I will keep you all posted and thank you!!

 

ok so swapped the new Vss to a Motorcraft vss. No joy On Christmas Day. Still no cruise, speedo, hard/late shift. I did not see any visible obvious issues with the wiring. Fuses are good. Don’t know much about a tone ring or how to test that.

 

You need to test the wiring. It is FAR more likely to be the cause than the tone ring. Looking at the wiring to find a problem is a waste of time. You won't see the problem, you need to find it electrically.

Disconnect the PCM and the VSS. Probe the BACK of each connector, not the end that makes the connection. Check both wires for the VSS for continuity from the PCM connector to the VSS. Also check for continuity to ground for each wire, and for continuity from each wire to a +12V source.

 

Maybe this will help.
Attachment 277289

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Thanks for all the advice and things to test. I am not too sure I understand exactly how to test them but i wanted to add some additional info. After changing the VSS to the MotorCraft part I backed it out of the driveway and drove about a quarter mile around the block and saw nothing register on the Speedo so i parked it again nad it sat for another day. When it was time to drive 65 miles home after 10 mins on the road i noticed the speedo was working and the ODO was counting again.. I was shocked to see anything moving. It worked for a few minutes before it got erratic again and jumped up and down like crazy before it went completely dead again. The trip was over 1 hour. Occasionally after it being dead it would work for 30 seconds to a minute or 2 and then fail again. I suppose it had to be something that i touched yesterday which was the VSS and visually inspected the harness that travels toward the front of the vehicle. I slightly lifted the wiring following the frame rail while i was looking for a problem. So, I guess that confirms an issue with the wires, a short or a bad ground. I don't know if i can find that on my own without having someone trace it for me. Hopefully they can understand that diagram better than i can. This thing is a real pain but i need to be able to drive this vehicle. Can i do any additional damage while it is behaving this way. Between 1- 2 is the hardest shift point, after that its not bad especially once i am on the highway and in 3rd etc.

 

Do you have a volt/ohm meter first of all and a basic idea of how to use it? Because trying to do anything without it is just not going to work.

It is OK to say you don't, but don't try & dissemble

You literally have the best group above in this forum on your thread here to help you & this is going to be the deal breaker if you can't or won't try.

Good luck.