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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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  #1  
Old 09-22-2008, 10:15 AM
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Problem with spedometer

This weekend on my 95 F250 I had an error 3 code flasing on my mileage display, so I went through the information and steps here to clear that:

http://www.ford-trucks.com/forums/27563-error-3-a.html
http://www.ford-trucks.com/forums/582067-error-3-a.html

I also removed the instrument panel from the dash to see if I could find a lose connection as, sometimes, the display would go blank and the speed indictor would go back down to zero while driving. I think this is how the CAL got reset but not 100% sure as I didn't find anything suspicious after removing the instrument panel

Yesterday, after resetting the CAL, the error 3 didn't appear any longer but today when I drove it for the first time I see the speed indicator bouncing around a bit. So if I am going 20 MPH it isn't steady and will sometimes go to 30 MPH or down to 15 MPH.

Does anyone have any information as to what might be wrong now?

If I had to replace the speedometer cluster, would the mileage be the same? Does that get stored in the computer and not someting in the cluster?

Thanks.
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  #2  
Old 09-22-2008, 11:10 AM
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The item we are talking about is the "PSOM".
A bouncing speedometer is usually a dirty VSS sensor in the rear end, some times you can take it out and wipe the filings off of it but if this is the case you have problems in the rear end. Also the tone ring might not be aligned right.

The speedometer is just a voltmeter and a good indicator of the information coming out of the PSOM.

If it is not in the rear end check the wiring from the rear end to the dash and unplug the ABS module and see if that helps.

If not replace the PSOM and recalibrate it.

You can get one installed by a Ford dealer ($$$) but they will not sell you one.

These PSOMs were upgraded in 1994 but any PSOM should work from 1992-1996 from an F-series, E-series or Bronco.
I have not heard anyone say they have found a PSOM that did not work from the other years yet.
Just get a cluster out of a salvage yard, pull the PSOM out of it and put it in your cluster.
Note that the PSOM that you put in will have the mileage on it that the truck you took it out of had.
Note also the Government frowns on this swapping on the mileage basis and may be illegal.
But a lot go ahead and do it anyway, not that I am telling you to.
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  #3  
Old 09-22-2008, 11:19 AM
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I understand what you are saying about the VSS sensor but I didn't mess with anything there. All I did was remove my instrument cluster, check for probs, put it back and reset my CAL. My speed guage was working fine before all of this happened.

Would that VSS sensor cause the odometer and speedometer to shut down while driving the truck? That sometimes happened prior to me getting the error 3 code.

Thanks for the advice so far.
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Old 09-22-2008, 11:35 AM
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Quote:
Originally Posted by JoeVB View Post
Would that VSS sensor cause the odometer and speedometer to shut down while driving the truck?
IT can but the VSS sensor itself very seldom goes bad. It is kind of a magnet sensor counting the teeth on the tone ring.
The VSS sensor can have junk on it as I said above to cause this non operation.

Other things that can cause this non operation are:
1) Bad wiring under the truck.
2) ABS module.
3) PSOM
4) Fused power supply to the PSOM.

Photo of the PSOM.
Click the image to open in full size.

Diagram of the VSS sensor.
Click the image to open in full size.
/
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  #5  
Old 09-22-2008, 11:42 AM
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while I had the instrument panel apart I also had the PSOM out, just like you have it there. I had it completely disconnected.

Would that have caused any of this?

Another question? Would it hurt anything if I took the PSOM from my 92 F150 and put it in there just as a test? That might help me isolate things.
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Old 09-22-2008, 12:11 PM
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Quote:
Originally Posted by JoeVB View Post
while I had the instrument panel apart I also had the PSOM out, just like you have it there. I had it completely disconnected.

Would that have caused any of this?
No it should not cause any problems.

Quote:
Originally Posted by JoeVB View Post
Another question? Would it hurt anything if I took the PSOM from my 92 F150 and put it in there just as a test? That might help me isolate things.
It should work OK.
Let us know what happens.
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83 F150 Flare Side 351W AOD
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  #7  
Old 09-23-2008, 09:49 AM
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slight update...

when I drove home from work yesterday (I also tacked on an additional 20 miles driving around to various places) I noticed there was no problem at all with the speedo so the problem must only happen when the truck is cold. My drive to work in the morning is only 3 miles so there isn't a lot of time for the truck to warm up and I did notice the problem this morning on the way in.

When I come to a stop the idle goes way down and then comes back up, this only happens for a second and then when I start to accellerate I get some hesitation and then I am on my way. But, when the truck is cold, the speedometer jumps around like I mentioned yesterday.

I am not sure what this means, just thought I would throw it out there.
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  #8  
Old 09-23-2008, 09:48 PM
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i removed the old VSS and looked in there, there was no apparent problem. After I put it back in the ABS light won't go off and the speedo doens't work at all.

I went to the parts store and found a replacement but it was a bit longer, kind of like what is in the picture that is posted. The area that goes into the differential isn't as long as that.

Not sure what the deal is and not sure why the speed sensor now won't work.

I might just end up taking it to the mechanic and letting him sort it out.
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  #9  
Old 10-03-2008, 11:01 PM
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I was looking at this tonight and both of these just fell off the board so I am pretty sure these are what is causing my problems.

I looked at each under a 10x eye loop and got some numbers off of the top. I THINK they can be identified. If I canít fix this I will need to get a new one.

(see red arrows) - ImageShack - Hosting :: dsc02313pt4.jpg
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  #10  
Old 10-17-2008, 10:16 AM
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ok, I am thinking this is fixed since I have been driving the truck for a few days with no issues.

On the board are several capacitors, they were falling off. The big chip in the middle with the X across it was also falling off due to poor soldering when it was assembled.

My friend was able to solder them all back on for me and, at the cost of me owing him lunch instead of $250 for a new one, it seems to be good now.



Thanks everyone
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  #11  
Old 10-17-2008, 11:39 AM
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Excellent sluething.

It seems to be a problem more closly related to the 95 model year.

My 95 had bad PSOM too. I think I'll go take a closer look at it and see if I can repair it.

Thanks man!
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Old 12-12-2010, 08:36 PM
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I am also looking into a kind of similar problem on my 04 F150 5.0 A/T truck. I get very intermittent idle issues when coming to a stop. The idle begins dropping rapidly and it stalls. fordfuelinjection.com reveals that if there is a loss in VSS signal to the PCM, the IAC slams shut and it wont idle. it happens usually 3-4 times almost every day but its random and most of the time it idles and decells just fine. I also find that I have to hold the throttle wide open to restart it faster. it will restart but cranks longer at closed throttle. I scanned the truck today with a snap-on handheld and had an intermittent code for the VSS CKT failure cleared it, did a couple of other minor repairs and it did not return. I have recently replaced all the vacuum lines, PCM relay, t-stat back to factory set temp, adj TPS, cleaned throttle body and EGR ports, Reset base idle, and timing back to OEM spec, I also replaced the PCM for another issue it had. it fixed almost all my drivability problems except this idle curse. I also figured out that the replacement engine done by the previous owner has the wrong cam for this PCM (old firing order) and I am wondering if this also is a possible cause. I am trying to get it back to base factory tune or a starting point.
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Old 12-12-2010, 08:36 PM
 
 
 
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