I changed out my tires for larger ones last year and also changed my gauge cluster in my dash so that the panel showed flames instead of being stock. When I did that I had to take my pointers off and then I put them back on when I did that I moved the pointer to more closley match my actuall speed but it is still off is there a easier way to try to get it closer to my speed then trial and error doing this??

 

This is from Steve Baz site for 94-97 trucks. I'm not sure if it will work or you can do it on your 2000. Please note you can only do this 6 times and then you have to replace the module.

Recalibrate Your Speedometer After Changing Tire Size

There is no tire size/code chart because tire size vs. actual tire dimensions are different between manufacturers. Even between the same tire size and same maker there will be a difference in actual size between the different tread designs.

The Ford calibration equation is:
20186 / tire height in inches = some number, then: some number /.6666 = program code

Example:
Start with 20186, divide by actual tire size in inches. Divide again by .6666

You want to use a rolling measurement to get your actual tire height (If you try to measure the tire in the driveway, use conversion charts, or anything else you will end up with an inaccurate reading again). Use your rear tire since the sensor is located there. Mark the ground and your tire and roll forward 3 times marking the ground each time. (I ran over a spot of oil at a local gas station and measured between my tread mark prints), then divide that number by three to get the average length of one revolution (this will protect yourself against a bad reading using just one revolution). You can then divide the length of one revolution by 3.14 to get actual tire height. Be careful in your measurements, a small amount will change the code. EX: 31.69" tire height is code 956, and 31.21" tire height is code 970.

Now, to program it into your truck:


Warning: You can only change the calibration 6 times without replacing the module.

To set the calibration, ground the single wire connector under the glove box it says PSOM (Programable Speedometer Opdometer Module). ”Yes there is only one and it has a spade type plug on the end". I used a wire with clips on both ends to ground the plug to a screw under the dash or try a test light and use the clip end to the PSOM and the other jam in a dooe hinge. Now look at your speedometer on the face of your dash while sitting in the drivers seat and there should be a "reset" button and a "select" button. While holding the reset button in on the trip meter, turn the ignition to 'on' while the wire is still grounded. Let go of the reset button. The speedometer display will sweep once and will show a code of some kind then push in again the "reset" button and the existing code will be displayed with RECAL?, mine said 976 RECAL? Now you enter your new code you came up with by dividing the rolling measurement by PI or 3.14 by pushing the "select" button until it gets to the new calibration code number. You may have to push “select” a whole bunch of times until you get to your code. If you turn off the key at this point the original code will not be changed or any of the 6 lives will not be used. To store your new code press “Reset”. Turn off the key. Unplug the ground wire. To check the new calibration, use the mile markers on the interstate. Run an indicated 60 mph and it should take exactly 60 seconds to go 1 mile.

 

thanks a-lot I will try this and see if it works. I wont have time untill tues so I will try it then thanks again

 

sorry just checking if my avatar is working good luck with the speedo

 

Try borrowing a hand held GPS. Calibration of your speedometer will be a snap.Baldeagle

 

Did the above procedure work for you, I changed my gauge face as well, my problem is that I got the speedometer right on up to about 35 mph, then it starts to get way off, traveling at 75 as indicated on the speedo, the GPS says I am doing 63 mph. I trust the GPS more than the truck, Before when it was at 75 I was going 71 according to the GPS, that I could live with but more than 10 off at 75 really sucks.

 

The 99+ trucks don't have a PSOM. The gauges in the instrument cluster are magnetically driven and can not be calibrated. You can however, get the ABS or 4WABS module recalibrated at the dealer using the following:

Special Service Message 11789 & 11790 from 7/29/99
1. Ensure all harness connections are plugged in.
2. Using NGS and version 3.2 or higher service card, plug into the DCL connector.
3. Turn key on w/engine off.
4. Select service bay functions.
5. Select ABS module or 4WABS module depending on application.
6. Select tire size/axle ratio configure.
7. Select tire size. If tire size is not listed use formula of: 63360 divided bt the circumfrence of the tire measured in inches. Add 2 zeros in front of the solution. Enter this number into the NGS as the REV.PER MILE figure.
8. Select tone ring size and verify that 120 is programmed in.
9. Select <option> and press TRIGGER.
10. Select <vehicle> and press TRIGGER.
11. Press <done> and the module will be reprogrammed.
12. Check speedo for accuracy

Circumfrence is 2PI x Radius.

 

Is this possible on 38.5's? I would like to also install the flames guage face and I would like my speedo to be accurate. I have had so many of these big ones, I usually just use the tach

DewaltKid,
Where did you get your guage face? Brand? Cost?

 

You can also reprogram your tire size and axle ratio using the WDS (Ford's current scan tool nightmare). Under Module Reprogramming, select Programmable Parameters and enter the information you want to change. Doing the change this way will also ensure that your trans shift points (if you have an auto) are correct. The axle ratio information is simple; just plug in what gears you're running. For tire size, the easiest way to go is to find out exactly what information you need - depending on the year of the PCM, it may be tire height, rolling circumference, or tire size (in millimeters) and aspect ratio - and call the tech line for whatever brand of tires you're running. Most of them are more than happy to furnish you with technical details.

 

after my gear change last week ford reprogramed my truck for the 37s and 430 gears. according to the gps i was 4mph off. with my superlift tru-speed i was able to dial it in perfect its dead on now

 

When you calibrate your speedo, you need to know revolutions per mile for your tire size. I've learned that you cannot input a number lower than 600, the PCM simply will not accept it.

Example: my stock tire size is 265/75r16 and 648 revolutions per mile, and my new tires are 325/60r20 and 586 revs per mile. 600 is as close as I can get, and really it's not off by much at all. BTW, 600 is approximately a 35 inch tire diameter, so if you are trying to calibrate for anything much larger (ie: 38's), you'll need the Superlift Truspeed.