Anyone know how to change the electronic speedo on a 94? I went to lower profile tires and am now off about 10%. In another post "nomo" said he had the instructions for fixing this. Does anyone know what they are or what formulas to use? Thanks

 

Hi BrianM,

All of the pre-1999 F-150's use a standard reduction gear in the tailshaft of the transmission which you can change for that purpose. Other reductions gears are available for about $17 or so at any Ford parts counter.

On some of those early to mid-90's vehicles, there is a way to adjust the spoeedo calibration on the back of the unit, but in all honesty I couldn't tell you the details on that.

If nomo doesn't have that info, it might be worth a quick call to your local Ford service department to check on that, to see if yours is one that can be adjusted on the back of the cluster.

Good luck!

 

Hi Mike

Thanks for the reply. I have checked the tailshaft and all that I have found is a plastic plug, where I believe the gear you are talking about, is supposed to be. I think the sensor is in the rear axle along with the anti-lock brake sensor, but I have know to be wrong. If in the axle, is there a gear in there?

Also thinking about a chip some day, so will be getting in touch with you on that. Was going to clean up the engine bay a little and delete smog pump and EGR and was wondering if a chip would eliminate the computer checking on these sensors and the subsequent check engine light from coming on. If it can be done, is it more money to customize the chip this way?

Thanks again, BrianM

 

I believe you are right Brian. My friends 94 flareside has the plug on the tranny and sensor on the rear end. But I am sorry I cant tell you how to recalibrate it.

 

Finally got everything figured out ( Thanks Rich ). Found info on Ford-Diesel site and it worked for me. So, for anybody that cares......

To recalibrate your speedometer after changine tire sizes:
Start with 20186, divide by actual tire size in inches. Divide again by 66.66.

Example:
20186/34.5=585.10/66.66=8.78

Thus for 34.5 inch tires, the calibration is 878.

To set the calibration, ground the single wire connector under the glove box (mine was light blue and yellow, check schematic in your manual for your application), hold in reset button on trip meter and turn ignition to ON. After speedometer needle cycles from 0 to top speed and back to 0, press reset button again. You should now see the calibration # that you currently have. From here, use Select to get proper calibration and press Reset to store.

When you press select the # only goes down, but don't worry if you need a higher number. After you get to about 400 or 500 ( wasn't paying as much attention as I should have) it will start back to the highest number speedo can be calibrated with. Mine was 1100. You can keep going from there.
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Lessons Learned by me.

If you go with larger tires, # will be smaller.

For my 275-50 15's the # was 1172, so I set the # at 1100 and it is only off about 1/2 mph at 60 which is alot better than it was.

If you shut ignition switch off before you press reset to store the new calibration, # will stay what it was before you started.

With stock 235-75 15's # should of been about 1044, but was set at 972 from factory. So, from day one, I was putting more miles on the odometer than was true.
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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.

Hope this helps,

Brian

 

Thanks for posting that. I printed it out so I will have it for future reference. By the way; are most of the speedometers off like yours was. if so-that sounds like a serious problem for ford if the word got out. just wondering

 

word of caution:

you can only do this adjustment 5 or 6 times before it wont ever let you do it again, something when it first goes into programming mode tells you how many times you have either done it, or how many times you have left, i forget.

 

Hi Brian M,

Great, & thanks for posting that info, and your results. that will be very helpful to owners of those model year trucks. Speaking of that, did you happen to discover the exact model year ranges that use that module by chance?

 

the PSOM system is used in :

92-96 F150
92-97 F250,350 HD
92-97 Aerostar
92-97 Econoline