Speedo help
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More Turbo
Joined: Dec 2007
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From: Umicorn UtopiaFantasyLand
Speedo help
Was going down the interstate today and speedo needle pegged past 85 and stayed for about 10 minutes, and the odometer numbers went blank in that window. All other gauges worked, and then come back to life again and kept working. has done this a couple times in the past 5 weeks, does bounce every now and then on smooth highway. Thanks for any comments. 
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
Sounds like lack of power to the PSOM (loose connection).
If the needle is passed the half way point and you lose power to the PSOM the needle may fall to the peg on the right side.
Losing power to the PSOM will also cause the display to go blank.
But as noted above it could also be a bad PSOM with a loose component on PSOM board.
If the needle is passed the half way point and you lose power to the PSOM the needle may fall to the peg on the right side.
Losing power to the PSOM will also cause the display to go blank.
But as noted above it could also be a bad PSOM with a loose component on PSOM board.
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More Turbo
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From: Umicorn UtopiaFantasyLand
Thanks you guys. The PSOM carries the mileage numbers,etc, and what else doe it do? Can the PSOM be repaired? I want to keep my origional mileage,etc. I also want to switch clusters and go with one that has a tach. I got one to switch the clusters the exchange. Can R.T. Grim Company fix the PSOM's? Not sure what I can do to keep original mileage,etc.
Senior User
Joined: Jun 2014
Posts: 466
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From: NE Ohio
PSOM REPLACEMENT F150 1995 photo series, step by step
The link I just posted provides a detailed write-up on replacing/repairing our trucks' PSOM. You can try to re-solder all of the connections, as a loose component could be causing your issue. Optionally, you can replace the unit as a whole, but you are correct as it would change the mileage being displayed. The PSOM also has a lot to do with your transmission. That is why I replaced mine. Hard shifts & blinking overdrive light. Subford probably has a more detailed description of everything the PSOM controls. I am also not 100% sure, but I think adding a tach cluster is plug and play. I picked up a few complete clusters with PSOMs, both with and without tachs, and they appeared to be exactly the same the last time I looked at them. Again, not 100% sure. My truck had a factory equipped tach cluster.
The link I just posted provides a detailed write-up on replacing/repairing our trucks' PSOM. You can try to re-solder all of the connections, as a loose component could be causing your issue. Optionally, you can replace the unit as a whole, but you are correct as it would change the mileage being displayed. The PSOM also has a lot to do with your transmission. That is why I replaced mine. Hard shifts & blinking overdrive light. Subford probably has a more detailed description of everything the PSOM controls. I am also not 100% sure, but I think adding a tach cluster is plug and play. I picked up a few complete clusters with PSOMs, both with and without tachs, and they appeared to be exactly the same the last time I looked at them. Again, not 100% sure. My truck had a factory equipped tach cluster.
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
Not very easy as the parts are not easy to come by except by taking them from another PSOM board. The parts are also surface mounted. The input diode can get hot and drop off the board and the main CPU can also come loose from the board.
1996 may also work with the 1997.
I do not know anything about the R.T. Grim Company.
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Cargo Master
Joined: Mar 2007
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From: Arcadia, Fla
As long as the PSOM's EEPROM is not bad, you can unsolder it from the old PCB and put it the new PSOM. That will keep your mileage and ratios correct for your truck. I did that when my E350 bus speedo went nuts.
Also look at the PSOM for the leaking capacitor, that is a major failure on the PSOM besides loose solder connections.
Also look at the PSOM for the leaking capacitor, that is a major failure on the PSOM besides loose solder connections.
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More Turbo
Joined: Dec 2007
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From: Umicorn UtopiaFantasyLand
PSOM REPLACEMENT F150 1995 photo series, step by step
The link I just posted provides a detailed write-up on replacing/repairing our trucks' PSOM. You can try to re-solder all of the connections, as a loose component could be causing your issue. Optionally, you can replace the unit as a whole, but you are correct as it would change the mileage being displayed. The PSOM also has a lot to do with your transmission. That is why I replaced mine. Hard shifts & blinking overdrive light. Subford probably has a more detailed description of everything the PSOM controls. I am also not 100% sure, but I think adding a tach cluster is plug and play. I picked up a few complete clusters with PSOMs, both with and without tachs, and they appeared to be exactly the same the last time I looked at them. Again, not 100% sure. My truck had a factory equipped tach cluster.
The link I just posted provides a detailed write-up on replacing/repairing our trucks' PSOM. You can try to re-solder all of the connections, as a loose component could be causing your issue. Optionally, you can replace the unit as a whole, but you are correct as it would change the mileage being displayed. The PSOM also has a lot to do with your transmission. That is why I replaced mine. Hard shifts & blinking overdrive light. Subford probably has a more detailed description of everything the PSOM controls. I am also not 100% sure, but I think adding a tach cluster is plug and play. I picked up a few complete clusters with PSOMs, both with and without tachs, and they appeared to be exactly the same the last time I looked at them. Again, not 100% sure. My truck had a factory equipped tach cluster.
I really appreciate that link! I've been studying that tonight. Glad you mentioned the transmission. My truck has a C-6. Does the PSOM have any signal to that or is it all mechanical as far as the tranny? I have a GearVendor O/D unit, which has it's own computer. GV O/D goes into O/D at 40mph. I had my C-6 rebuilt last year. On a couple of occasions recently, my tranny would go in reverse but not go backwards, just whine somewhat,would do the same in forward gear. I turned off the ignition and restarted and all was fine. Immediately went into reverse and all was well. Haven't mentioned this to my tranny builder yet. Thanks!
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More Turbo
Joined: Dec 2007
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From: Umicorn UtopiaFantasyLand
As long as the PSOM's EEPROM is not bad, you can unsolder it from the old PCB and put it the new PSOM. That will keep your mileage and ratios correct for your truck. I did that when my E350 bus speedo went nuts.
Also look at the PSOM for the leaking capacitor, that is a major failure on the PSOM besides loose solder connections.
Also look at the PSOM for the leaking capacitor, that is a major failure on the PSOM besides loose solder connections.
Will do, thank you!
Senior User
Joined: Jun 2014
Posts: 466
Likes: 1
From: NE Ohio
Subford is correct. The C6 is not, I have an E4OD which is. However, PSOM swap/repair should clear up the problem you initially posted this thread about. You're very welcome for the link - I used that link the first time I did one and it helped a bunch.
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