1998 F150 Speedometer error

So, I have the 98 F150 4.6 parked for 6 weeks whilst I go overseas. When I come back, I noticed the speedometer is reading about 10% high (ie. when I am going 70mph by the speedo, I am actually travelling about 63 mph according to timing the mile markers).

Would disconnecting the battery cause the computer to lose the speedo calibration? The engine runs fine, no MIL. Any other thoughts? Bad VSS? The tires on the vehicle are slightly larger than stock so I would expect the speedo to read a little low.

TIA

Reply to
David M
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On Wed, 11 May 2005 10:08:51 +0000, David M rearranged some electrons to form:

Well, I took it to a speedo shop, they put it on their dyno, and, it was dead on. I would not have thought that the stretch of highway that I chose to do my timing apparently has mile markers that are not placed accurately. Weird. I tried it on a different highway and, yes, apparently the mile markers on that stretch of highway were different.

Reply to
David M

Bro,

I recently installed a Tru Speed speedometer calibrator when I upsized my tires on my Superduty, and I can't find any mile markers near me that are accurate. I-96 between Novi MI and Brighton are especially off.

I think it's set a little low still, and my GPS died several months ago, so until I replace the GPS I'll be off a little...

Reply to
Matt Macchiarolo

On Thu, 19 May 2005 14:15:25 -0400, Matt Macchiarolo rearranged some electrons to form:

I searched for a little while and could not find any accuracy specs for mileposts.

Reply to
David M

Some quick math (described in the TruSpeed docs) will get you pretty darn close.

I used my GPS to get mine dialed in. It's dead on accurate when the tires are new, but reads high as they wear and the diameter decreases. :)

Reply to
invalid unparseable

Yep, that's what I did, and my miles per tank came back to about where they were before the tire replacement...between the tire replacement and the Tru Speed install, my miles per tank decreased by almost 50 miles...I was going the same distance, but the odometer were clocking more slowly, so after a tank of gas it appeared like I didn't go as far...which is about 300-320 miles unloaded in mixed but primarily freeway miles.

When I get a new GPS I will dial it in exactly. My Jeep is still off by about 10% since the large tires and final ratio change, even with the recommended speedo gear replacement...I'll have to tweak that one of these days with a different speedo gear, which is a lot easier to change out than installing a Tru Speed but harder to adjust. :-)

"The OTHER Kevin in San Diego" <skiddz "AT" adelphia "DOT" net> wrote in message news: snipped-for-privacy@4ax.com...

Reply to
Matt Macchiarolo

Given the work ethic of many state DOT workers, or their lowest-bidder construction contractors, do you think that two damns are given about the accuracy of mileposts?

I'm sure there are hard-working, diligent highway construction workers out there. Just too damn few of them.

And for the record I always slow down in construction zones. :-)

Reply to
Matt Macchiarolo

I also lost about 50 miles/tank, but I'm pretty sure it's due to the big tires and increased rolling resistance. (And probably the tweaked ECM I run too.. ehhe)

Had to do that on the 4Runner when I bolted the 33's on it. PITA to say the least...

Reply to
invalid unparseable

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