92 F150 with 4.9l engine. When I bought the truck I was told that one of the previous owners replaced the engine and tranny and thats whenthe speedometer starting working wrong. It is at least 10 mph off when going 60 mph. It also racks up a lot of extra miles on the odometer. Does anyone know how to fix it.

 

This aught to do it for you: https://www.f150forum.com/f10/bigger...reading-35549/

 

My tranny was replaced. Would this still need the same fix

 

If it's erratically inconsistent, you have another problem. If it's consistently off, it just needs to be re-calibrated, the method dependent on type. Mechanical or electronic.

 

so when I went to this page you posted I got a how to seafoam your engine, wtf? it was interesting and I would like to do it to mine but it wasnt relevent to this post, must have been a glich in the system or something, I'm so confused, lmao

 

It, must be a glitch. Nobody else mentioned this occurance. Maybe try it again. Either way, Seafoam your engine!It's really fun & good for your engine too! And while I'm at it, what's with the WTF? Does your mother know you type like that? I'll bet not!!! I have half a mind to call her and if the other half shows up, I just.................. nevermind.(it's probably long distance)

 

Where is the "PSOM"

 

roflmao! well as far as the glich, its in my brain, and my mother well, she probley can see me typing this right now, she passed in 99' but she would be laughing at this thread just as I am, so don't feel bad, I think she would have liked you as I do,

 

I don't remember how to do it, but there is a way to reprogram the electronic speedometers just by pushing the odometer button or something like that. The instructions are posted somewhere in this forum.

 

The transmission and or axle ratios will not affect the speedometer on the electronic PSOM trucks. They get the signal directly from the axle rotation, the best bet is that the PO had larger tires on it and was programed for those tires, larger tires will cover more ground for each revolution making the truck think that it is going farther than it actually does.