Hello from Texas...new to this forum. I recently purchased a pre-owned 2019 F250 Lariat 6.2L after recently selling my 2013 F250 6.7 Powerstroke. Now on to the issue....when I purchased the truck a few weeks ago, it had just a few miles over 10K on it and looks/runs like new. However, while using my Waze app recently, I noticed that there was a variance in my speedo speed reading and what the Waze speed showed. Generally, the difference ranges from 7-10% , with the higher variance at higher speeds. The truck has stock wheels and tires (verified), so that is not the problem. The other part of this is that the problem is not constant....about 50% of the time, the speed is spot on (in addition to Waze, I also use an app that provides a GPS speed reading that I compare to my speedo speed). After doing a bit of research on the internet, I find nothing other than comments related to the increase of wheel/tire size effecting speed readings and the need for calibration. I then disconnected the battery to see if it could possibly be an ECU issue. After reconnecting, the speedo was right on. However, after parking and then leaving again...the speedo was off again. So the issue is random....sometimes speed is on, sometimes off.
I've called and spoken to 2-3 service advisors at local Ford dealerships, and none say they have heard of this issue. One stated that it is possible the prior owner may have installed larger tires, had the truck recalibrated for the larger tires, and then before trading it in put the original tires back on but did not have the truck calibrated back to the original tire size. That might make sense....if the speedo was consistently off at all times. But again...the problem is intermittent.
Any ideas or recommendations? I really do not want to take my truck to the dealership and be without it for the "several days" that each advisor told me it would take for them to diagnose and test to try to determine the problem. My experience has been that "several days" usually means a week or two based on my prior dealings with the SD's.

Just looking for input on potential causes, as I have found that the feedback from forum members is typically much more helpful than that of those at dealerships. It's not that big of an issue, as I just turn the GPS speed app on and watch my speed using it when driving, but I know there is going to come a time when I don't do that and get nabbed and a ticket for speeding.

Any constructive input or advice would be appreciated!

 

Might be that the previous owner changed the tire size to larger tires in forscan. When he sold it, put the stock wheels and tires back on without changing forscan back to stock? Is it 7-10% slower on the speedo...?

 

would make sense if the speed variance was constant. However...sometimes the speed is right and correct, other times it is off. So...if it had been previously recalibrated for larger tires, the speed would be consistently off when driving.

 

https://www.google.com/search?source...4dUDCAc&uact=5

Wasn't that difficult on Google.

 

ok...but This occurs without Waze being connected via Apple CarPlay, AND the speed is compared using an app that specifically does nothing but provide current real time GPS speed.

 

Ur putting all ur faith in a app, and disregarding the possibility of the truck being correct.


I would venture to say the truck is right.

If the VSS was or is incorrect, the truck would show other symptoms since shifting and multiple other controls are based off speed.

 

actually, putting faith in two different GPS-based apps. As well, and I should have included this in my original post, I had my wife pace me on the freeway in her car and my speedo was off. So...unless both GPS apps are wrong, as well as my wife’s vehicle speedometer being wrong, there would seem to be an issue with my speedo reading.

 

https://www.gps.gov/systems/gps/performance/accuracy/

If your confident with a (upto) 95% GPS accuracy that your truck is wrong.

You didn't say if it was reflecting a higher or lower speed, a 10% increase in false speed would represent increase mileage then actual mileage. About 6000 miles over 60,000 miles and vice-versa the other way.

 

My truck speedo is showing me going slower than I actually am. When my speedo says 65 mph, GPS shows I am actually doing 75 mph+\-

 

Try again with your phone not plugged into your car charger (running off battery) and report back.

I similarly shat my pants when I brought my truck home and did the same thing. Small wonder, it doesn’t matter what app you’re running. Your phone will use the telemetry from the truck when it’s plugged in via usb (and there is a known bug). Silly me, I thought it would just be staying charged.

 

Here is my suggestion.

Note ur speed and RPM's and truck details or just your rear end gear.

Depending on gear ratio in top gear, a 6.7 will spin at 2000 RPM's @ 70 MPH. Many members here have posted pictures of speed and RPM, compare against what you have.

 

Was it a Canadian Imported truck?

 

When all else fails there's always setting the cruise at 60mph, the stopwatch on your Iphone and a couple mile markers to get accurate speed.

 

Thanks for all of the feedback and suggestions. I will be away for then next week..will update situation when I have something to update with. Thanks!

 

Something to consider..
The faster you go the more noticeable to difference will be.

This is an example of stock tires vs 37x12.5
Speed: 20 30 40 50 60 70 80 90
Actual: 21.5 32.6 43.4 54.3 65.1 76 86.8 97.7