Classicfordguy
Full Access Member
Well I tried to racalibrate the speedometer/Odometer today in my 94 F250 to compensate for larger tires using the procedure bellow, for one reason or another it did not work.
I measured 3 rotations of my 37" which came out to 317.5" divided by 3.14=101.1 then drop decimal and 1011 is my new constant. Well the odometer read the new constant now if I ground the wire and check it but the speedomerter is very wrong. Using another car to test, at 45mph it reads 40 and at 55 it reads 47.
Has anyone else had success with this procedure. here it is.
Thanks,
-Rob
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Recalibrate Your Speedometer After Changing Tire Size
#1 Measure your tires with 3 rolling stops by marking your tire with a piece of chalk and the ground. Make a mark at each 360 degree rotation until you did 3.
#2 Measure the distance of the 3 lines you made and then divide them by 3.14. (mine was 301 divided by 3.14 = 95.8) or 958 by dropping the decimal.
#3 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.
Warning: You can only change the calibration 6 times without replacing the module. Your Ford dealer should be able to do this for you too if you aren't comfortable doing it yourself.
I measured 3 rotations of my 37" which came out to 317.5" divided by 3.14=101.1 then drop decimal and 1011 is my new constant. Well the odometer read the new constant now if I ground the wire and check it but the speedomerter is very wrong. Using another car to test, at 45mph it reads 40 and at 55 it reads 47.
Has anyone else had success with this procedure. here it is.
Thanks,
-Rob
----------------------------
Recalibrate Your Speedometer After Changing Tire Size
#1 Measure your tires with 3 rolling stops by marking your tire with a piece of chalk and the ground. Make a mark at each 360 degree rotation until you did 3.
#2 Measure the distance of the 3 lines you made and then divide them by 3.14. (mine was 301 divided by 3.14 = 95.8) or 958 by dropping the decimal.
#3 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.
Warning: You can only change the calibration 6 times without replacing the module. Your Ford dealer should be able to do this for you too if you aren't comfortable doing it yourself.
