Hey guys. I have been driving my truck for almost a year with the lift/tires/gears in it and I have not had any problems. While on the internet last night I read some information on this speedo calibrator:

http://broncograveyard.com/bronco/i-...calibrator.htm

At first I thought I didn't need one of these since I have just compensated in my head for the speedo change. Actually I found out what my real speed was versus what the speedo says with a GPS. Anyways, while I was reading about the speedo calibrator it says that this would be needed since the truck is thinking that it is going slower then what it really is, so when I am doing 100 km/h the speedo says 80, so the truck thinks I am doing 80. The site said that then the computer would not be putting in the right fuel / air mixture (mine is a 96 with MAF). I was wondering if then the computer is thinking that my truck is lagging so it pumps in more fuel. With the gears that I put in, I am in the right RPM range for the speed (2200 rpm at 105 km (65 mph)). I am getting good milage right now (16 mph) on the highway.

So I guess my question is that since I did the gears and the RPM's are where they should be, does this mean that the computer is taking this signal, or is the computer taking the signal from the speed of the tires? Is the sensor in the rear dif or the tranny? I have the M5OD tranny, stock 8.8 rear. And ultimatly, is this something that I should look into buying?

Thanks for the help.

 

on a newer 8.8 there should be a VSS vehicle speed sensor right on the front of the rear chunk. some older trucks use a cable and speedo gear right in the t-case.

i cant see the computer having problems from doing gears and tires. too many ppl do these kind of swaps and i havent heard of any problems. however you might try this method, this is what i did on my 96 PSD and didnt have to buy anything extra.

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.

-cutts-

 

Sweet. Thanks for the awesome info. I learned a ton. I will do this once I get my summer tires back on since they are the biggest difference from stock.

Thank you for taking the time to post this info.

Jim