Speedo issue???
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Joined: Sep 2010
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Speedo issue???
I recently bought a '97 F150 2WD, 4.2 V6 and am having speedometer issues. Its not that the speedo doesn't work, its just that it registers a slower speed then the truck is actually going. For example, when the speedo registers 35mph, I am actually going 41 (6 miles over) and when it registers 70mph I am actually going 82 (12 miles over), so as u can see the gain is a direct ratio. From what I can tell this is also throwing the odometer off a little. I feel like this would be caused by an equipment change that did not match stock specs but I don't really know much about it. I do know the tires are the proper size. Can u tell me what may be causing this? Is the sensor bad? Did someone put a different rear end in the truck? What is the most likely culprit? Thank you!
Postmaster
Joined: Nov 2006
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From: SE Wyoming
If the tires match the door sticker that leaves the gears. For '97s you can change the VSS gear but I don't know which color one you'd need to get close to the right reading. FWIW your odo will also be reading 15% off as you thought.
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Joined: Jun 2009
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If I had to guess I would say the gears have been changed. But, I would have thought on a V6 that someone would have put 4:10 gears in instead of the stock ones and that would have caused the speedo to read higher than actual speed since the speed is from a pickup inside the transmission based on revolutions of the output shaft. With 4:10 gears you would be turning more engine rpms for the same speed. So - I doubt anyone would have put a 2:73 gear or something like that in the truck.
Did you buy from a dealer or individual? Can you find out who the last owner was and see if they can tell you what the deal is?
My real guess would be they had larger tires on the truck and had a recalibration done for the speedo. Then they removed the large tires to sell but had no way to recalibrate the computer back to stock. If you purchased from a dealer see if they can check the computer or reinstall a stock tune.
If all else fails, purchase a tuner for your truck. That will allow you to reset the tires and gears to the correct stock settings. Gears should be 3:08 I think for your truck.
Did you buy from a dealer or individual? Can you find out who the last owner was and see if they can tell you what the deal is?
My real guess would be they had larger tires on the truck and had a recalibration done for the speedo. Then they removed the large tires to sell but had no way to recalibrate the computer back to stock. If you purchased from a dealer see if they can check the computer or reinstall a stock tune.
If all else fails, purchase a tuner for your truck. That will allow you to reset the tires and gears to the correct stock settings. Gears should be 3:08 I think for your truck.
Senior User
Joined: Jun 2009
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Sorry I missed that. Did not realize 97 was not controlled by computer.
I would still guess that someone had larger tires on at one point and in this case swapped the internal gear to compensate.
Now with stock tires - you need the original gear in the tranny for correct speed.
I am sure someone on here can tell you what the stock gear color is and how to check yours. Just make sure you ask the question in terms of transmission speedo gear so they don't think your talking about rear end gear.
I would still guess that someone had larger tires on at one point and in this case swapped the internal gear to compensate.
Now with stock tires - you need the original gear in the tranny for correct speed.
I am sure someone on here can tell you what the stock gear color is and how to check yours. Just make sure you ask the question in terms of transmission speedo gear so they don't think your talking about rear end gear.
