my 2006 5.4 f150's speedo is incorrect. lower speeds 40-50 it says imgoing about 3 mph faster than i really am. then up at like 70-80 its says im going around 6-8mph faster than i really am. i checked this with 2 GPS's that read the same, and put them in other vehicles and were dead on. but not in my truck. even unprogrammed my programmer and its still the same. any help?

 

Have you changed tire size? It is normal for the truck speedo to be 2-3 mph fast at abput 65 mph. 6 to 8 sounds as if the tire size may be off.

 

https://www.f150online.com/forums/20...eters-off.html

Known issue.

 

everything is stock besides intake, and straight pipe exhaust and programmer. stock factory tires. iv drivin next to my girl friend on the highway and i was goin 80 and she was going 72......... on top of the times i got off readings with the gps

 

Ok, does the tuner tell what size tires it is set for? If not, return it to stock and check it, see if there is a difference.

 

the SCT tuner has an adjustment, but it says "rev/mile" im assuming means revolutions per mile? i wouldnt even kno where to begin changing that.

i did return the vehicle to stock, unprogrammed it is exactly the same

 

i just googled revs per mile and found a calculator, my 275/65 R18 should be 629 revs per mile. il change that and see if it does anything.

 

629 will get you close, but that number is based on the unloaded tire circumference. Multiply it by 1.03, 1.04, and 1.05 (3-5% squish factor) and try those numbers.

 

i re-programmed it to 629 and was still like 4 mph off around 40 and 50. i just kept increasing it by 10 rev/mile to see where i could get it. right now im at 670 rev/mile and its real close atleast at 40 and 50mph maybe only still 1mph faster than the gps....i may increase it +5 and see if that will make it dead on, i still need to test it on the highway too.

kinda weird how its like that, why wouldnt they just make the ****in thing work correctly to begin with i dont feel like paying ford money to fix somethin that i shouldnt even have to deal with. thanks for the info guys

 

I went from a 265/70/17 tire to a 285/70/17 tire, what, 1.5"-2" higher and now my speedo is almost dead nuts on, truck says 69mph I'm doing 70 (GPS). Trying to keep us honest they are.

 

yeah i just found my extended warrenty will cover the speedo, im gunna bring it in and see if they can fix it so when its not programmed it will still be accurate.