I recently purchased a 2003 Screw. Subsequently I discovered that the speedo is about 15mph faster than actual. I purchased a used one from LKQ and quickly discovered that you can't change without assistance of dealer to reprogram.

Thus,the purpose of this post. I called service mgr and explained problem regarding speedo to which he suggested that I bring the truck in and they could determine the problem. So I took truck in for service and after a day in service, the service rep. called and said that cluster was defective and they could not fix. I explained that I had a used cluster to which qhe said that if I would bring it in they would switch old for new(used) and make it compatible to system. After another day in service they called and said the truck was ready. So I went in picked up the truck and took out on freeway along with GPS app and to my surprise the replaced speedo showed exactly the same 15mph over actual. Called service rep and he simply said that there were a lot of variables that could effect overage, i.e., gear ratio, tranny, etc.

What am I missing, is there no way to fix speedo and if so why did I go through the expense and two days of truck in service to find out that well that's the way it is.

 

Sounds as if you have smaller tires than what the computer is programmed for. If it has the stock tune, the tires could be shorter. If it was tuned and had taller tires in it, they may have left the tune in but out the shorter tires back on. Could also be that the rear end was changed and had lower gears than original.

Can't believe the dealer didn't mention those.

 

Thanks for reply. The first thing I did was to replace tires with new OEM spec 255/70/16 thinking that this would make sure speedo was correct. I am not sure if rear end has been changed but I have appointment with rear end place to check. If I have known tire size and known gear ratio can the dealer tune the speedo to the correct calibration?

 

It seems some dealers can, some can't. You can buy a tuner that has the capability and get the bonus of better performance.

 

Responses are greatly appreciated. Do you have a recommendation since I am clueless as to this technology but am working diligently on the learning curve?

 

Tires will not make 15mph difference.

 

I think if it had bigger wheels and 3" taller tires it would.

 

gears alone would do that

 

Not even close. Do the math. They would have to be about 7 1/2" taller.

 

No way! Do too much math with my work. I'll take your word for it. Since the clustèr is digital, can't believe the dealer thought that would fix it.

 

Update: have found that this is a situation that if you cannot swim you will surely drown.

Decided to go back to service rep and ask exactly what happened the last two days. I asked to confirm that the cluster/speedo in the purchased truck was defective and could not be calibrated. Confirmed. So the second one was good. Yes, tested 100% positive. So if I had the tire height and gear ratio I could get my speedo working correctly. Well, no don't know about tranny and which gear it has so unless you figure that out you are going to be 12mph+ for the rest of your life.

When you are looking at the lifeguard with the buoy in his hand and you know he is not going to throw it to you, you quickly realize you are the only one that is going to save yourself. So I decided to order a Edge Evolution CS and get the speedo calibration ability plus all the other features.

However, this was another incredible journey.

 

S m h

 

OK, I guess I have to say something here. In his original post, the OP stated that his speedo had a 15 mph (fast) error. What we don't know is at what driving speed he is seeing this. If the error is at a real speed of 30 mph, then it's effectively a 50% error, which is huge. However, if he's at a real speed of 60 when he sees this, the error is reduced to about 25%.

And, we all know that Ford speedometers in F150s read about 2-3 mph fast anyway in the 70-75 mph region, due to mechanical errors in converting an electrical signal from the VSS to an analog readout. So, it's very possible the OP's error is really 12-13 mph, but again, we don't know the speed, so we don't know the percentage.

Let's assume he might be wanting to travel at 75 mph and is seeing an actual 12 mph error, which allows for a built in 3 mph fast reading. This equates to 16%. So, to correct his speedometer with tires, he'd need tires with a 16% larger diameter. The 255/70/16 tires he has on it now have a diameter of 30". A 16% increase would be tires at 34.8", pretty big, but not outrageous.

However, since he bought the truck used, the previous owner may have mounted larger tires and compensated for them with a higher gear ratio. And, he would not have had to have mounted tires that were 4.8" larger to do this. He could have gone up say, 2" and adjusted the gearing to match.

Regardless, a programmer should be able to compensate for an increased gear ratio and/or a changed tire size.

To the OP: try to get your speedo to read about 2-3 mph faster than a GPS reading of 75 mph. That should make your odometer read correctly.

- Jack

 

To be a little more specific as to incorrect mph, when I am doing 70 on freeway, speedo reads 85. And yes, it is my suspicion that indeed the previous owner may have had bigger tires and the requisite higher gear ratio.
However, in my experience you don't go to the doctor to confirm that yes, you are dying, but rather that you are in trouble but I think we can help/save you. Is it really relevant what the percentage is, or that I am still dying. I haven't bothered to mention that the used cluster has 123,000 miles and the purchased/title disclosure states 174,000 so guess what that does to title and sale ability? Surely if you can allow the substitution of one cluster for another in a Ford proprietary security program then can change the odometer. If I had purchased a brand new Ford cluster with 0 miles would that be the miles that I would start with making it a brand new truck?
I am not sure what the suggestion to have my speedo read 2/3 miles faster than 75mph is based on since at present I only have the benefit of the power of prayer, but as previously stated I have ordered an Edge Evolution CS so that I can control my own destiny. However, I will always wonder "what am I missing" if it had been a YUGO I would known I should have missed it.

 

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