That's actually a relief. Any thoughts on me not taking the RABS test connection apart while troubleshooting wiring? From the schematic it looks as though it might mess up testing for shorts between both RABS and the VSS from the PSOM side of things since I was testing mainly from the RABS plug up front.

 

As long as the RABS Module was unplugged and the PSOM was unplugged and The VSS sensor was plugged in and you took your readings from the RABS Data Link Connector under the hood it should have been right.

 

Yeah that's how things were done.

Well I'm using good 'ol RTV so I'm going to wait to drive it tomorrow and see if a simple diff oil change did anything. I doubt it. I might get another sensor tomorrow or order one even and see if that makes a difference. I got my from the local shop and it looked different but was the right part according to what I brought in and what they showed. The old one was enclosed in what looked like black plastic and had a dimple type pattern like a 3 gallon pot. Not sure how else to describe it. Reverse splines?

The new one was smooth but seemed to match up right in every aspect.

I'll know more tomorrow. Might do some more electrical troubleshooting this evening if the weather holds.

 

Another thing. I tried testing the connections at the RABS plug by the fender in several ways. Essentially, every combination of the PSOM, RABS, and VSS in/out. I got nothing. Should I have found a complete circuit in some of that?

I've checked the breakers, too, throughout this process to make sure I didn't blow anything.

 

So could this help? The yellow light was not on, and with no current coming up to the RABS plug while I drove the car up on blocks, that seems to mean that no current is making it to the RABS plug, right? Should I try to find current while driving at certain points in the circuit? Say, at the RABS then to the PSOM like the schematic seems to flow?

 

I think you took that statement wrong.
With RABS module unplugged the yellow light would not be on. I was talking about a statement you made before you unplugged everything that the yellow light was on.

I other words if you left the PSOM unplugged and plugged in the RABS module and the VSS sensor and drove the truck and the yellow light is on at that point that would mean it is not the PSOM that was causing the problem. This statement was brought about by the question you asked if the PSOM could be causing the all the problems.

By the way that is a limited slip rear end so make sure you put some Friction Modifier Additive in it if the oil you put in did not have any in it.

 

With everything unplugged there would nothing on the wires.
With the PSOM or RABS modules or both unplugged and the VSS plugged in and at about 30 MPH rear end speed you should get around 4 VAC.
You said you checked the wires already for opens, shorts to ground and for a short between the two wires. You said they all checked good.

There are no breakers or fuses involved with the two modules unplugged.

I know there are two different VSS sensors that look almost alike for this set up. One goes in the rear end (like the one on my 95 F150) and the other one goes in the back of the E4OD (like the one on my 94 F53). They drive the same type circuits (PSOM) but the F53 does not have an ABS on it, just the PSOM.

The one for the F150:

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I added the modifier and still have the issue of course. But, at least I can rule out the rear end mechanically.

But the yellow light isn't on. I think I mis-posted somewhere, but I can't find anything except in the original post where I said

The ABS hasn't come on except when I did the ABS test (grounding the plug and getting the code 16). Other than that, regardless of the configuration of plugs (and RABS module) I don't get the ABS light except when I turn the truck on and it comes on for a second or so then it's off. That's what got me thinking that if the RABS module is unplugged then I should see the light warning me about a problem with the ABS. But that doesn't happen. So does the PSOM control the ABS light? Because if it does, then would that point to a bad PSOM, no?

Or should I try to troubleshoot other systems somehow, like a bad signal going to the PCM?

Oh and my VSS matches that picture perfectly. I'm not sure where I got the idea that it was smooth but it isn't.

I've taken the truck on a few short test runs and it just shifts like crap, on again, off again, mostly on, and during deceleration to a stop sometimes it stalls out. Really getting the feeling that there is one simple solution we just haven't found yet. Very frustrating.

 

I've taken the truck on a few short test runs and it just shifts like crap, on again, off again, mostly on, and during deceleration to a stop sometimes it stalls out. Really getting the feeling that there is one simple solution we just haven't found yet. Very frustrating.

Its acting like that because the computer doesn't know how fast the truck is moving, maybe even if its moving.

You gotta get a reading from the VSS as posted by Subford, until you do its not going to work.

Long shot but the abs light might be on because of a bad connection at the master cylinder, connector under the middle of the tank. The slip on connector on the wires tend to corrode away.
I've had to cut that pig tail off other trucks at the bone yard to repair it.

However even if that is the cause of the abs light being on, it is not the reason for the shifting problems, at least I haven't seen it to do so with other trucks.

That just senses the fluid level, if the level drops the anti lock function is disabled to ensure full braking power, whatevers left of it in a low fluid condition, triggering the abs light to warn the driver.

If the connection at that connector is lost the same happens, anti lock function is disabled and the light comes on.

You gotta get a signal from the VSS, based on the thread here you haven't yet done so. You must be missing something in the testing of that circuit, sounds like you're doing it right but.....

Maybe get another meter and retest?

 

The ABS light can only come on with the RABS Module plugged in.
There is no need to look at the information going to the computer until the speedometer works.
You might want to read this PDF also:
http://7pt3powerstrokediesel.com/lit.../2007_1_04.pdf


RABS Light circuit:


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You did say the ABS had a bad fuse, try leaving the ABS moule unplugged and take it for a drive with the PSOM plugged in and see if the speedometer works then and shifts OK.

 

Tried that, didn't make much difference. I tried that and unplugging the PSOM to see if the truck ran smoother, nothing.

So, I hopped down to the Picknfool yesterday and they were having a half off sale! So I got another PSOM and ABS module from a 93. Put in the ABS, no difference. Put in the PSOM, BINGO.

PSOM bad! New one works great, and it's only 1500 miles off to boot!!!!!!!!!!!!!!!!! Yay!!!!!

Thank you, subford, for your patience while walking through this with me. The research and schematics you have are priceless. The whole fix cost me a total of $17 from the junkyard!!! I'm a happy camper now!!!

And as a side note, the truck is so much more crisp, much more powerful, so I know that thing had to be messing with a few other components. It ran like a 4 banger before, maybe a nasty 6, and now it runs like there is really a 5.0 in it. Whooooooo hooooooooo!