The PSOM's have capacitors on the circuit board. These capacitors will fail over time. It's not a Ford thing, it's just what they do. Nothing lasts forever. When these capacitors leak, they can ruin the circuit board. There are plenty of shops that can fix them. I have a local speedo repair shop [Tacoma Speedometer] that does a great job and I like spending my money locally when I can.

It just might be a good idea to take the PSOM out and look at the circuit board. If you plan on keeping the truck, just send it out and get it rebuilt. If it is not bad now, it will be.

 

The PCED is in digital format on AllData at your library
Once you are on AllData and select your vehicle, the PCED is in there under computer controls/ diagnosis and testing
It has all the pinpoint tests and all the flowcharts, fuel and ignition categories and all of that
Same with the EVTM it is in there under the wiring diagram and component locations sections
Back to your problem'
Most problems I saw was with the connector at the rear axle VSS (the wires break right near the connector after constant movement up and down)
Also the sensor itself, if it does not pass the resistance spec, replace it
I het new good ones at the junkyard, many have been replaced that you will find in junkyards

 

Code 452 Pinpoint Tests - Operation CHARM

 

1Butcher - Thank you, doing a visual inspection of the PSOM is part of my short term plan. I'm sure the landlady plans to keep the truck indefinitely. I am familiar with electrolytic capacitors failing or drifting value over time. I've done some vintage stereo repair, including re-capping amp boards. I may go through the board and check the caps, or just replace them if I happen to have the right ones. I will look into getting it rebuilt as well.
Just FYI, I have checked many of the old caps from the 70's and 80's stereos that I worked on, and found very few of them to have even drifted out of spec. I can't recall ever finding one that leaked and failed. I will not discount that possibility though.

ManicMechanic007 - Thank you, When I went to the library, I asked for help. The people that helped me seemed to be familiar with AllData, and said they did not have access to it. Maybe they have access to it and just don't know it, but it seemed like they knew what they were talking about. I like your suggestion about the connector since the problem is intermittent. I think one of the times it started shifting hard and the OD light started flashing, I had just gone over an overpass and the joint at the end coming off of it gave the truck a decent jolt. I will pay particular attention to the wires at that connection when I check out the wiring and plugs. Also, when it acted up that time, it started shifting like it was going into neutral for a little bit when shifting to the next gear, I didn't experience that when it acted up previously. I will also check the VSS again, I believe it was around 1800 ohms, but I'm not sure. I should have written it down.
BTW, I like your handle. I wonder how many people know where Manic Mechanic comes from.

rla2005 - Thank you for posting that information.

I appreciate all of the help.

 

I played with the truck some more last night.
I checked for radial play in the pinion shaft, I couldn't tell that there was any.
I checked the wiring from the VSS to the firewall plug. I jumpered the pins on the firewall plug and connected the meter to the pins on the VSS plug, set to ohms and enabled the tone. I wiggled the wires the whole length of the harness, especially by the VSS plug, never lost the continuity tone.
I checked VSS resistance at the VSS, at the firewall plug, and at the test plug, all readings were 1066 ohms.
I checked the output of the VSS at the test plug with the truck on jack stands and the truck running. Voltage and frequency reading rose steadily (as best I could tell) increasing speed from 0 - 30 mph. VSS readings were 0 - 6.1V, and 0 - 650 hz, as measured with a multimeter. I'm not sure what to make of the VSS readings. In my internet research I've found that resistance should be around 1400 ohms, and I've found that it should be between 800 and 1400 ohms. I've found that voltage should be 3.5V at 30 mph. I found another post where a guy said he had two similar trucks, and VSS output on both trucks was about the same as my readings. I test drove the truck some more last night, I still have not seen any problems with the speedometer, and I had no problems with shifting hard or blinking OD light last night.
I also pulled the plug on the firewall to the PCM, it looked good.
I have not yet pulled the PSOM to check it.
I'm wondering if I should try another VSS. If so, is there a preferred brand, or should I try a salvage yard? I called the local Ford dealer, I can't get one from them.

 

I would go through the pinpoint test steps for code 452
You may need a new processor
Your readings sound right to me without actually checking a manual
The pinpoint test steps will walk you through all of that

 

I haven't found access to pinpoint steps, the only diagnostic info I have is in the link that rla005 posted.
What processor? The PSOM? The PCM?
If my readings are good, and if the truck fails and goes into limp mode again, I believe I'm down to those two things.

 

The PCM / ECU
The pinpoint tests are in the PCED
You are down to the cluster, the processor the psom or the wiring (still)
Pinpoint tests are the only way to narrow the problem down
EVERY code has pinpoint tests in the PCED including no codes outputted even
I have 5 of them but no 1996 and they are VERY year specific for certain codes and problems
So, either find and buy an expensive 1996 PCED or get the info from AllData at your library free
One look inside a PCED, and you'll see thousands of pinpoint tests

 

Having the electrical issue occur after hitting a bump could point to loose or corroded ground connections. Check out posts 6 and 7 at this thread Ground Points - Ford Truck Enthusiasts Forums https://share.google/bcUIPWP8uqD8A4IJC
How are the connections at the battery terminals and the fender mounted starter relay?
I also have asked at my library about repair manuals and all data. They don't have it.

 

Cleaning the grounds sounds like a worthwhile thing to do, I know they can cause problems.
The only source I've found to get the pinpoint tests in the PCED is a friend that is an adjunct professor at the local university, but that won't be until October.
I pulled the PSOM, it looks fine. I pulled the two caps and the varistor and checked them, they tested good. I may pull the PCM and give it a look. I may also look for a PCM and a PSOM to swap in for testing. I'm also thinking about buying an o-scope, I want one anyway.

 

That link is the Pinpoint Tests for Code 452.

 

I bought an O-scope. This looks like a possible cause to me. I haven't had a fault since I disconnected the Speed Control Module, but I haven't driven the truck much since I disconnected the module.
Anyone have any experience with the output signal with the Speed Control Module connected / disconnected? Maybe this is normal?
I'm going to try to drive the truck more with the module disconnected.

Regarding following the pinpoint steps. Thank you for posting the DS1 chart, but I don't have a breakout box, I don't know where the test pins are for the resistance check, and I can't go to DS4.......................


PSOM output with Speed Control Module connected.

PSOM output with Speed Control Module disconnected.

 

You bought an oscilloscope, now buy a breakout box?
Or
You can just back probe both components to do the same thing without one
I have one and have not used it in 20 years
Your '96 F250 should be OBD1 with a 60 pin processor and uses the 60 pin breakout box
If you lived near me, I'd just let you use mine
My breakout box is old and hammered, has at least one pin that does not work (EVP pin I believe)
We all learned to backprobe EVP's first for that reason
That is also the reason I got the old one when the dealer I worked for got a new one
They are on Ebay cheap at times, just like the NGS youi need

 

The PSOM outputs a square wave, 0-5V.
I don't see a difference with your two osc images, what are you seeing as different?

 

In the picture with the Speed Control Module disconnected, the peaks are relatively flat. In the picture with the module connected, the peaks taper toward 0 volts.