Driving today, my truck seemed to be surging a little on cruise control (it was/is quite windy today 40 MPH +so that may be part of the surging). I also noticed that the speedometer is accurate up to 40 MPH. Above that it runs faster than I am going according to GPS. At 45 it is 1 mph high. At 65 it is 4 MPH high.

I have a 94 f250 2wd 7.3 idi trubo with 410 gears and an e4od.

Where does the speedometer get its readings from? I cleaned the VSS on the rear end but it didn't change anything.

 

could be as simple as you have slightly bigger tires than your gear is calibrated for. My speedo reads progressively higher from 35mph and up. It's because my tires are beasts.

 

Oversize tires will make your speedometer read LOWER than your actual speed, unless you recalibrate the PSOM. And yes, it does get the speed from the VSS. If the speedometer isn't fluctuating, the VSS signal is most likely good, and you just have to contend with the fact that our speedometers are not all that accurate.

 

The tire size is the size it was delivered with, but they are worn. I measured the circumfrence and recalibrated, but it is still off a few MPH. I don't want to make another calibration until I replace the tires because I only have 4 more calibrations.

Is there any way of resetting the amount of calibrations?

 

yeah, i totally misread the OP's post. Thanks for clarifying.