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post #1 of (permalink) Old 11-15-2001, 07:20 PM Thread Starter
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Recalibrating the speedo

Anyone done the recalibration on their Bronco after getting larger tires? I found a tech article explaining how it is done, but I am just not following where the wire or connection is that needs to be ground before you turn on the ignition and play with the reset dials. I'm also not quite following the math in the article for the re-computation. This of course is the procedure for the newer electronic readouts. I don't want the dealer doing it for $120 if I can handle myself.

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post #2 of (permalink) Old 11-17-2001, 12:24 AM
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Re: Recalibrating the speedo

All I can remember is the wire to ground is by itself between the ashtray and glovebox.But be careful because the e-prom chip or whatever it's called can only be reprogrammed 5 times then will need to be replaced.

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post #3 of (permalink) Old 11-18-2001, 12:14 PM
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Re: Recalibrating the speedo

Where'd you find this article? There was a thread about it a while back in which I posted the Ford procedure I got from another source. Have you read it?

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post #4 of (permalink) Old 11-18-2001, 09:33 PM
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Re: Recalibrating the speedo

Swamp Donkey (from the forum) has a page on it, and his math is as follows:

Tire Circumference = Tire Diameter x 3.1416 (Note that this does not take into account the squat of the tire when loaded. To allow for that, I used a tire diameter of 41", although the actual height was 41.5")

Revolutions per Mile = 63,360 / Tire Circumference in Inches

Conversion Constant = Tire Rev per Mile x Teeth on Sensor Gear / 8,000

(The number 63,360 is inches per mile; 8,000 is a the number of pulses per mile the PSOM needs to be accurate.)

The number of teeth on the sensor gear in an 8.8" is 108. Instead of figuring your revs/mi, you might try looking them up on the tire MFG's page... it's more accurate (unless you know your exact tire diameter).

If you want to see his page, it is HERE.

He has some really cool custom fabrication stuff on his page.

As far as the wire, it was just a grey plug with a single wire hanging under my glovebox somewhere, and said PSOM on the side of it in white letters. Just take a wire and stick it in there, and then stick the other end of a good ground... just get a long wire and hook it into the battery ground clamp.

You probably can find the button pushing procedure, if not just ask.

Your Toy is loaded huh? Does it have Power Engine?

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