Possible Bad PSOM
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Possible Bad PSOM
On my 94 f150 I'm having bad tranny shifting problems. My speedo needle goes all wacky after 50mph. I had the tranny looked at by a certified shop and they said my tranny is fine and that it may be a PSOM. Does anyone have any input on possible things I can check out. Also it has about 152,000 miles on it
Postmaster
Joined: Nov 2011
Posts: 3,533
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From: SW Florida
I've also had the RABS controller screw with the PSOM. Try unplugging it and going for a drive.
The module is behind the glovebox. Empty all the stuff out of it, squeeze the sides inwards, and let it drop all the way open. Right in front of you you'll see a black module about the size of a paperback book (not exactly that size but maybe a little wider) with an electrical connector or two. Disconnect those and go for a drive.
The module is behind the glovebox. Empty all the stuff out of it, squeeze the sides inwards, and let it drop all the way open. Right in front of you you'll see a black module about the size of a paperback book (not exactly that size but maybe a little wider) with an electrical connector or two. Disconnect those and go for a drive.
Mountain Pass
Joined: Jul 2014
Posts: 244
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From: Minneapolis & Terlingua
I just went through this with my 93 F250. The most common culprit is the toner ring in the rear pumpkin.
In my case I replaced the VSS. The old one had a slight groove in it on the magnet face...made no real difference. Then I had the PSOM rebuilt...made no difference. Then I probed the PSOM feed wire from the VSS and the signal out wire from the PSOM and the signals both looked fine.
Next step and was toner ring. When I took the diff cover off, the toner ring had chipped/dented teeth and the pinion gear had a big chunk broken out of it. I ended up putting a new diff in, plus new toner ring, and the issue was solved. Speedo is now rock solid.
If you are interested I posted some tech articles here: https://www.ford-trucks.com/forums/1...-2ed-gear.html
In my case I replaced the VSS. The old one had a slight groove in it on the magnet face...made no real difference. Then I had the PSOM rebuilt...made no difference. Then I probed the PSOM feed wire from the VSS and the signal out wire from the PSOM and the signals both looked fine.
Next step and was toner ring. When I took the diff cover off, the toner ring had chipped/dented teeth and the pinion gear had a big chunk broken out of it. I ended up putting a new diff in, plus new toner ring, and the issue was solved. Speedo is now rock solid.
If you are interested I posted some tech articles here: https://www.ford-trucks.com/forums/1...-2ed-gear.html
Fleet Owner
Joined: Aug 2005
Posts: 23,666
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From: Easton,Ks
The only thing that can be rebuilt in a PSOM would be to replace the caps or re-solder some loose parts. I have seen the main PSOM chip have some of its many solder points come loose from the board and also some of the large parts.
Dose your truck vibrate very bad over 50mph?
If not I would look at the rear end first.
Dose your truck vibrate very bad over 50mph?
If not I would look at the rear end first.
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I found someone parting out a 93 f150. Would be a good idea to pull the part from his truck and put it in mine
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Mountain Pass
Joined: Jul 2014
Posts: 244
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From: Minneapolis & Terlingua
FWIW. If you decide to have your PSOM remanned you should use RT Grim. They're in PA and were the authorized Ford PSOM repair shop...they have all of the Ford test equipment. Look up "Fordclusters.com"
I had my PSOM serviced by D&D Instuments in MN...about two miles from my office. They charged me $239. RT Grim charges $279 which includes shipping both ways.
With all said...it's probably your toner ring.
Best of luck.
More Turbo
Joined: Jun 2012
Posts: 520
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From: Deepwater Mo.
I replaced the VSS...The wiring...Even replaced the entire speedo cluster...
It ended up being Just a little bur on one of the teeth on the tone ring made the needle bounce at 50 mph.... The pinion bearing crapped out on me a few years back and some metal pieces must of been left behind in the diff to cause it to burr.
Was a easy fix....Basic hand tools, jack-stands ect... Flat head screw driver and a hammer was all I needed to chisel the tone ring off and hammer the new one one on after pulling the diff.
Just keep every thing clean and dirt free and put it back together the same way it came off.
You do not have to pull the ring gear off...
It ended up being Just a little bur on one of the teeth on the tone ring made the needle bounce at 50 mph.... The pinion bearing crapped out on me a few years back and some metal pieces must of been left behind in the diff to cause it to burr.
Was a easy fix....Basic hand tools, jack-stands ect... Flat head screw driver and a hammer was all I needed to chisel the tone ring off and hammer the new one one on after pulling the diff.
Just keep every thing clean and dirt free and put it back together the same way it came off.
You do not have to pull the ring gear off...
Mountain Pass
Joined: Jul 2014
Posts: 244
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From: Minneapolis & Terlingua
Dude...you are likely doing a lot of extra work.
To properly test you need to hook up an oscilloscope to the wires at the PSOM...really hard to do when driving. I did this and it was a waste of time. If you insist make sure to back probe and to NOT puncture the insulation. I posted a picture of the oscilloscope screen from the ATRA article in the other post referenced which will show you what the signals should look like.
The pros at RT Grimm told me that 60% of the time that the cause of the needle fluctuation is most likely the toner ring in the pumpkin. They were right on.
The toner ring was the cause with mine as well as with the other posters speedo.
We both spent a lot of money and time on things that did not necessarily need replacing.
To access the toner ring, take the rear cover off the pumpkin and examine the ring. Even the smallest dent/chip will cause the needle to bounce around.
The toner ring is only $30 or so through autopartsnation.com.
To properly test you need to hook up an oscilloscope to the wires at the PSOM...really hard to do when driving. I did this and it was a waste of time. If you insist make sure to back probe and to NOT puncture the insulation. I posted a picture of the oscilloscope screen from the ATRA article in the other post referenced which will show you what the signals should look like.
The pros at RT Grimm told me that 60% of the time that the cause of the needle fluctuation is most likely the toner ring in the pumpkin. They were right on.
The toner ring was the cause with mine as well as with the other posters speedo.
We both spent a lot of money and time on things that did not necessarily need replacing.
To access the toner ring, take the rear cover off the pumpkin and examine the ring. Even the smallest dent/chip will cause the needle to bounce around.
The toner ring is only $30 or so through autopartsnation.com.
More Turbo
Joined: Jun 2012
Posts: 520
Likes: 4
From: Deepwater Mo.
On mine, the faster I went past 50 mph the further it bounced. at 90 mph the needle would be all over the place. Like he said jack the truck up.
Put it on jack stands...
Take the diff cover off and inspect every tooth on the tone ring very carefully. One bad tooth can make that needle bounce.
Postmaster
Joined: Nov 2011
Posts: 3,533
Likes: 17
From: SW Florida
Yeah but disconnecting the RABS module takes all of 30 seconds. To R&R the diff cover and inspect takes what, 10 minutes plus the cost of fresh lube, friction modifier (if limited slip) and RTV? I suggested the RABS module because like you, I've already done the signal circuit testing, and that module was what I found bad on my truck. It was screwing with the signal so I unplugged it and all was well. Can't hurt to try it first. It's FREE!! 