U7153 - Speedometer Calibration

[Jetpuffd]

On my 1999 Expedition I’m having a heck of a time nailing down the speedometer. I am running Hankook DynaPro MT’s in 315/75/16. Hankook publishes the revs per mile as 601.

My U7153 device has been updated to 9r04. When I plug in the 601 revs per mile and ‘enable’ the change, run the installation, I’m way off. Roughly 25% off on speeds. So I compensated and turned the revs per mile to 751 and I was much, MUCH closer but this is not correct.

Can someone advise me on what the issue here may be?

[mikel]

maybe the setting for gear ratio is wrong now that you enabled the VID block?

Try entering the current/factory gear ratio and revs per mile then load the tune.

[Jetpuffd]

Factory gear ratio is 3.55. Predator only lets me enter 3.54 before moving up significantly higher.

[mikel]

3.54 is fine...

[Jetpuffd]

So I reuploaded the stock tune and then the modified tune and I’m still having this problem. No codes are being thrown by the computer and the PCM is new. Again, any idea what may be going on here?

[mikel]

OK, my bad....you said 3.55 was stock, so you should not be making any changes here

Go back to stock then reload the tune and dont mess with axle ratio, and it should be fine.
You only need to adjust that if you change the gears in the truck from what it came with stock.