Ok this is getting frustrating. 1992 f250 w/5.8 and E4OD 2wd. I have a 452 code-VSS and the hard shifts from 1-2 and 2-1. I have pulled the diff cover off and changed the fluid and inspected the tone ring. Looks good. Replaced the VSS with a Motorcraft one and Ohmed it out to under the hood and to the back of the PSOM. Had 1400 ohms everywhere. Replaced the solenoid pack, trans fluid/filter change and wired in a new plug for the solenoid pack because the plug looked a little sketchy. I have replaced the PSOM with a refurbished one. I cannot get rid of the 452 code or the hard shifts. I also have a RABS light that sometimes goes off but will not produce a code either when I follow the procedure for code retrieval. Are they related? If I unplug the RABS module behind the glove box the light stays off(obviously) but there is no other change. I am losing patience with this thing. Anybody have any ideas where else I can look or any other testing I can do to get this thing sorted? Thanks in advance.

 

Hard 1-2 shift can result from the MLP being defective. Check ohms in each gear at sensor, or replace it. Not sure if this will set 452, depends on what a flow chart wants tested. There are posts on here with ohms charts. Also need explanation of 452.

 

mlps was answered in his other post about 452, post #2, should stay with one thread so people know what you have already done

E4OD issues and turn signals? - Ford Truck Enthusiasts Forums

 

Continuous Memory DTC 452 indicates the PCM detected an error in the PSOM output signal during the last 40 warm-up cycles.
Possible Causes:
-- Damaged Rear Anti-Lock Brake Sensor.
-- Damaged PSOM.
-- Damaged harness circuits.
-- Damaged Powertrain Control Module (PCM).

Ok we know it is not the PCM or the Transmission causing the 452.
I have no idea what ohm charts you are talking about for a PSOM.

With the RABS lamp on you have a problem between the RABS/PSOM and the rear end.
Most likely you have damaged harness circuits. under the truck going to the rear end.
The VSS may have the wrong gap space also.

 

I did not see another post. Was MLP changed or checked?

 

Also signal between PSOM and PCM has to be checked with a signal wave tester.

 

Just looking over your post, and my little pea brain is confused. You say unplugging VSS does nothing. I have a 92 E4OD, and if you unplug the VSS, lt will snap your neck on 1-2 shift. Are you clearing codes after each attempt? Just trying to be helpful. Good Luck

 

Update. So far I put in a new MLPS, double checked the wiring from the diff to the ECM. Pulled the ECM and looked inside. Found some corroded and leaking capacitors and ordered and installed a new one. I have also installed a new MAP sensor and TPS. Still hard shifts and occasional RABS light. The VSS is seated down on the diff housing like it should. I don’t see any kind of adjustment there. Would the RABS cause the hard shifts? Could I bypass the RABS? Could I jumped out the RABS sensor to see if that makes a change or test it? I presume that’s the sensor that’s inside the driver frame rail adjacent to where the MLPS is located correct?

 

You can unplug the RABS module to see if that helps.
Yes the RABS module can take the DSS (VSS) signal low and cause the hard shifts.

 

Guess I've been lucky in that regard. Have a very common ABS light, only going out occasionally. But other than when I removed my cluster and went for a short drive, my trans shifts very normally. Or at least normal from what I presume is normal for an E4OD.

Good luck. That little bit of hard shifting I went through with the cluster removed would be VERY annoying to live with all the time.

Paul

 

Is it possible someone reset the PSOM? Check reset changes left, and multiplier number with OEM calibration. To me, with cluster removed, the whole apple cart is upset. Just a thought.

 

You would have hard shifting and the speed control would not work either with the cluster removed (1992+ trucks).
Their is no reset for the PSOM and the number of changes would not matter either.
The calibration would not matter either unless it was set for the F53 then it would be way off and hard to change the calibration.
The calibration would only effect the right speed indication of the needle and the distance that you traveled.

 

The PSOM is a “new” refurbished one. It came with 63 miles on it with 6 resets left and already calibrated for the stock sized tires which I have on the truck. I did unplug the RABS module behind the glove box and went for a quick drive up and down the street. It seems to be a little better on the 1-2 and 2-1 shifts. I will have to drive a little longer to really feel it. Maybe it will settle down a bit more. It is a new ECM too with only a couple of drives and less than 10 miles on it. When I changed the fluid I used the Dex III/Mercon universal ATF and now I am wondering how much difference it would make if any if I put the latest version of the mercon V.

 

Just went for another ride. Still the same. No change. I guess I was imagining the shifts being a little better.

 

Ford no longer makes mercon fluid. Any name brand marked as such will work fine. Also the ABS light will come on if the rear light harness has any faults disableing rear lighting.