I am looking for information on how to go about reprogramming the speedometer on a 99' F-350 with 35" tires. At 70 mph I am really doing about 80 mph and all of my shift points are off, I have called about six different dealers and no one can give me a definite answer one said it is not possible, one said I can change the driven gear, and the others said they can reprogram it to Ford's spec's. but not for that big of a tire. Any help would be appreciated---Thanks

 

It's really easy. You need to figure out the revolutions per mile of the tire you're using. The Ford computer can go as low as 601. Have your dealer reset the computer to what ever number you come up with.

 

Here is some Info I saved from one of the other message boards here... I hope this helps.

>>>
. "RE: Speedo Calibration"
18-Dec-00, 08:23 PM (EST)


Pete
Changing your gears will not affect you speedometer.Changing your tires (height) will throw off the speedo.I used the following to recalibrate my Bronco with excellent results.
Just one word of caution the module can only be programmed 6 times
Locate the dealer mode programming enable single-terminal connector. The
connector is located at the bottom of the instrument panel below the center
of the glove box. On all vehicles, the dealer mode enable wire is Circuit 567(LB/Y).
Insert a jumper wire or alligator clip in service wire and clip other end
to vehicle ground with the key in the OFF position.
Turn key to RUN while holding down the trip odometer RESET button on the
speedometer. Release RESET button.
The Speedometer will prove out(sweep across dial and back). The
English/Metric and revision levels will be displayed. The last number of
the display id the dealer mode lockout count. This count shows the number
of allowable conversion constant changes remaining. When the count is zero
(0), no additional changes can be made to this instrument cluster. If a
revision is required a service instrument cluster must be ordered.
Press and release RESET button again and PSOM conversion constant without
the decimal point will be displayed followed by the word CAL.
The new conversion constant necessary to correct the speedometer can be
found by determining the current percentage error. One way to do this is by
comparing the indicated miles versus mile markers on an interstate trip.
The longer the trip, the better indication of the error since interstate
mile markers are not always exactly 1 mile but the average is very close to 1 mile.
Going to taller tires (indicated miles less than true miles) will mean the conversion
constant must be reduced by the same percentage as the speedometer error and
going to smaller tires (or a numerically higher rear end ratio) means the conversion
constant must be increased.

Press and release the odometer SELECT button as many times as necessary to
change the conversion constant to the correct value. The constant will only
increase (not decrease) when the SELECT button is pressed so reducing the
constant means counting up until the constant jumps to the bottom of the scale
and begins counting up from there.
Note: Pressing and releasing the RESET button to lock in the new
conversion constant reduces the number of times the PSOM can be
reprogrammed by one count. If you change your mind and want to go back to
the old conversion constant, turn the key OFF BEFORE you lock in the new
constant.
When the new correct value is displayed in the odometer window, press and
release the RESET button to lock in the new conversion constant.
Turn the key OFF and disconnect the ground wire and check to see that the
speedo works correctly.


Joe
94 Bronco XLT,5.8,E4OD <<<<


__JOHN__Õ¿ö
Member-
"Crusin North" Car Club
Santa Rosa, Calif.
72 F-250
ICQ#6030753
https://www.ford-trucks.com/pictorial/big/1972_f250_2.html

 

The above cut & paste only applies to a PSOM (programmable speedometer odometer module) cluster, a 99 and later Super Duty has a standard cluster. I'll almost guarantee that 35" tires are way below 601 revs, thus the speedo and shift point will still be off.

 

So, for those of us with larger tires than that, I have 39"s.. is it possible to get the calibration correct?



2001 Monster F350 CrewCab 4X4 7.3 PowerStroke, Bright Amber Metallic, 12" lift, 39" Mickey Thompsons on Weld Typhoons..

 

39"? How many Honda's can you crush with that?

Unfortunately, no, you won't get a calibtarion for that to work. You can change the speedometer drive gears to get it more accurate, but the shift points and other PCM stuff will still be off.

 

Most 35" tires are right at 600 revolutions per mile. BFGoodrich lists their 35" Mud Terrain at 596 and Yokohama says theirs are 604 or there about so you could get it close. As for changing speedo gears, do these new ones even have those any more?

 

Honda? Oops.. what honda.. you mean that civic speed bump? Bummer, I'll have to get with the stealership to find out how close I can get the speedo... the whole "really officer, I have no idea how fast I was going" does'nt really fly...

-Ry
2001 Monster F350 CrewCab 4X4 7.3 PowerStroke, Bright Amber Metallic, 12" lift, 39" Mickey Thompsons on Weld Typhoons..

 

I have alot of experience with building trucks using 35" tires. They are my preferred tire size on all of my trucks. generally starting with 4:10 gears. If you want to do a complete job correctly and retain your original gearing and fuel consumption, take my advice. Change your ring and pinion gears to 4:88's . This will put you within a point of your original gearing and you will pick up uour original mpg and power. When you go to tires over 33" you break the gear curve and your gearing yourself to high. Now your having to put your foot to the metal and by doing so raising your rpms to turn those big tires. in the case of the new powerstroke you won't notice the power drop as much, but it's there. I've never had to change my speedometer gear at the tranny because this combination has put me practically on the money. Good luck.

 

Ok, I have done the reprogramming in my 95 F-150 to match my 33's and it seems to have worked as far as I can tell. My Uncle has a 90's Mustang with the E4OD tranny and I think that he has the digital dash cluster. Would the reprogramming sequence work for his as well since he changed tire sizes and his is off now? If it does, then where is the PSOM test cable located and what color is it?

Karl