Speedometer Inaccurate on '03 Sport

[briwayjones]

I got my '03 Sport used with 33,000 miles on it with the factory tires. And it still has factory size tires on it. From the very beginning the speedometer has been off. At lower speeds around 30MPH it registers as much as 3 or 4 MPH faster than what you are actually going. As you get to higher speeds, around 80MPH it's only about 2MPH faster than it should be.

I have determined this by comparing it to a Scangauge that I have hooked up to it. The Scangauge also agrees with speed radar boards I pass. When I have the Scangauge hooked to my '00 Explorer it matches that speedometer.

I know in different year Explorers Ford has changed the way it registers the speed of the vehicle. In older ones I think they used actual hard lines and speedo gears? On newer ones sensors in the transmission? Some of them use the ABS sensors? Since this is a '03 I'm thinking it might just have a bad sensor somewhere?

It's a 2003 Sport, 2WD, manual transmission.

 

[RomeovilleIL]

I suspect that is not an issue with your speedometer but instead with the scan guage readings. If the speedometer was off, it would be a % that was constant throughout the range ie 10% at 30mph = 3 off, at 80mph would be 8 off. Since that is not the case and your needle isnt bouncing around the speedometer is probably working correctly for the truck. A better test would be to take a test drive with your GPS turned on to get a live measurement of your speed from a different source. Accelerating and decelerating is not a good time to check speed as it may not be accurately tracked. Instead set a steady pace with cruise control and check for differences. If it is a constant difference, then there may be a ratio issue.

 

[swshawaii]

Please delete this reply.

 

[briwayjones]

I suspect that is not an issue with your speedometer but instead with the scan guage readings. If the speedometer was off, it would be a % that was constant throughout the range ie 10% at 30mph = 3 off, at 80mph would be 8 off. Since that is not the case and your needle isnt bouncing around the speedometer is probably working correctly for the truck. A better test would be to take a test drive with your GPS turned on to get a live measurement of your speed from a different source. Accelerating and decelerating is not a good time to check speed as it may not be accurately tracked. Instead set a steady pace with cruise control and check for differences. If it is a constant difference, then there may be a ratio issue.

I agree that it's strange that it doesn't seem to be a constant percent off. Which is why I was asking about sensors. But I'm sure that it's not the scan gauge. This is something that I've been dealing with and trying to figure out for 7 years. It's not a vehicle I just got and quickly thought something might be off and am asking about it without getting used to the vehicle. The scan gauge agrees with the speedometers on any other vehicle I use it on that I know the speedometers to be accurate to within about 1mph. It also agrees with permanently installed radar sign boards that I pass.

I don't have a GPS unit to test the speed with. But maybe I'll try to use my phone GPS which is the best I can do.