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Reprogramming For Tire Size and Gear Ratios


Xzibit A

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me
 


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ExplorerDMB

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Did you use the process that I described or a different way?

-Drew
 




Xzibit A

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i tried a differen way as mentioned above and thn did it your way, it was more accurate doing it your way
 




MoabB2

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Can this only be done for 98+ 5.0 Explorers? Or can it be done on a 97?
 




ExplorerDMB

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97 is still gear driven - you have to change your gear in your transmission
 




MoabB2

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ExplorerDMB said:
97 is still gear driven - you have to change your gear in your transmission
A gear in the transmission? Where can I find more info about this? Parts needed etc..?
 




Fredness

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I did, but I used the XCal2.
The problem is it corrects the shift error (speed vs. RPM) but not the speedo itself. Gotta get my hands on one of those tools, anyone renting out theirs? :D
 
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MoabB2

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Great! Thanks Brooklyn.
 




Fredness

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My local Ford dealer is going to do it for $45. MUCH cheaper than the tool ($1500) or the adapter ($100). I'll let you know how it goes...
 




MoabB2

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Be sure to let us know how it turns out!
 




ExplorerDMB

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$45 that is great.

-Drew
 




Fredness

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OK, dealer did it for $45 (+tax) and I have to take it on a test run tomorrow to see how accurate it is.

Here is what I've found (bear with me, my thought process is very linear):

Simple math:
Circumference = Pi x Diameter, so if I used 31, it would be:
31 x 3.14 = 97.34 and 63660 / 97.34 = 650.9 revs/mile

Little research + simple math:
But we know this is not correct, since the tire is 30.7" tall overall (no load).
30.7 x 3.14 = 96.39 and 63660 / 96.39 = 657.2 revs/mile

Little more research:
Well, the website lists the 31x10.50-15LT A/T TA/KO as 677 revs/mile @ 45mph, but at what pressure and what temperature?

Some real world data:
I decided to chalk test, only I used electrical tape for a smooth, definitive edge to measure from. I verified the cold pressure of 38 psig, and after 30 miles of highway driving it measured just shy of 40 psig (warm). While the tires were still warm, we rolled one complete rotation for a distance of 92.625", being sure to measure everything using the trailing edge of the tape.
63660 / 92.625 = 684.0 revs/mile!

Now, which one is right? Well, none of them.
When I test it tomorrow using the measured distance, I believe there is going to be two variables introduced that haven't been discussed at all in this thread (just hinted at here).

"Growing": As the tire spins faster the effects of centrifugal force move the tire walls outward and the tire grows taller with speed.

...and "Balance": if one side is at 38.0psig and the other is at 38.2psig, our L/S differential is going to "eat" some of that difference as heat, and the tone ring will show an average of the two tire circumferences.

Originally, we posted -5mph differences over a timed stretch and I was using my XCal2 to data-log the runs so the times are very close. We'll see how the actual road test does. I think it will be close enough to work, but there are far more variables in the process than we've covered so far. I need to find a way to get tone ring counts at speed!

I'm sure the 684 rev/mile number that we had flashed int he ABS module is dead on for the wife's tires, when hot and when the vehicle is at or near zero ground speed, on one side!

Anyway, does it matter? I think not. I just don't want the wife to get a ticket with the new tires reading 5mph slow.

Any takers?
 
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Fredness

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I guess not...

O.K., a 5 mile "Odometer test area" is 2 miles up the interstate from us, so on the way to meet a customer, I clocked the trip. 5 miles, zero error!

Then, on the way to dinner with the wife, she timed the same run at 60mph. 1.00.365 on the stopwatch! I can't ask for anything better. 100% pleased and the total cost was just over $50 after taxes.
 
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Nick26

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most of those just interrupt the signal from the VSS.

-Drew
does anyone have any idea if that signal is just straight voltage? i.e. 2V=10mph 12V=80mph ? Then I would think we could just either put a resistor/amplifier inline with the VSS and fix it ourselves. The other possibility is its an oscillating signal and that would take a bit more work to correct adapt.

I would think for the truspeed to be so universal it would have to be a pretty simple/universal type signal too.
 




rickcdewitt

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you probably don't need to worry about getting it perfect the first time as you can go back and change the revolutions per mile until its right.10 or 20 revolutions at a time?
 




Nick26

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you probably don't need to worry about getting it perfect the first time as you can go back and change the revolutions per mile until its right.10 or 20 revolutions at a time?
well i think i read somewhere else on this site that it can only be reprogrammed 6 times before its locked, not to mention if you paying a ford dealership to do it thats like $100 a pop.
 




rwenzing

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does anyone have any idea if that signal is just straight voltage? i.e. 2V=10mph 12V=80mph ?
No, it is a frequency.

In the case of a 98~01 Explorer, the raw pulse from the rear axle ABS sensor is used by the 4WABS Module to generate a 0~12v square wave that represents vehicle speed. This frequency of this square wave is read and used by the PCM, speedometer, speed control, GEM and, in some cases, the radio HU, Message Center, Automatic Ride Control and the overhead console.

The 4WABS Module can be programmed (using a dealer tool) to give the correct frequency-to-speed ratio for the tire size you are using based on the tire revs/mile. A correctly calibrated VSS square wave will have a frequency that corresponds to 8000 pulses per mile.

The above applies to 98~2001 Explorer. Other Ford vehicles may do the VSS conversion in a different module such as the PCM or the GEM.
 




emeterio

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I have a ford explorer 1999 xls that needs to get the pcm reprogrammed, I live in puerto rico and can not find someone to reprogram the unit, any suggestions, thanks
 


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