I was just curious if anyone here has calibeted their speedo/odo after a gear swap and/or tire change? If so, how?

I used the Superlift TruSpeed on my truck and I really liked the ease of install, not to mention unlimited calibrations.

Would this work on a 4JG2/UCS69/Isuzu. I see Superlift's application page, but no Isuzu. However, it can't be too far off from GMs wiring/computer system...?

I know many might not think the speedo being off as a big deal. But here in Japan that is actually one of the tests that is run for inspection during JCI time. I don't want to get pinged. Any thoughts on speedo calibration?

I should get under my truck and check, but while I'm here, is there an external VSS/VSSB? Is the speedo/odo run off the same signal to the ECM from a speed sensor?

There is a gps based speedo out that is doesn't matter what you do it's always accurate. I can't help other than say try a google search.

Joe

That brings up an interesting point. GPS will track the vehicle and report the true speed of the vehicle when the vehicle is in motion, right?

What about when the vehicle is put on a roller and tested? Since the vehicle is stationary, will the GPS still report an accurate speedo/odo reading?

no, the vehicle actually has to be in motion for the GPS to work. If the GPS senses that it's at the same coordinates as the last reading, then the speed is 0. If the coordinates are different, the GPS does a calculation based on the difference in the coordinates and the time between the samples it took and that gives you the speed.

Richard <img src="/forums/images/graemlins/patriot.gif" alt="" />

For all intensive purposes the GPS speedo would work 99.9 percent of the time.

Why would a 96 Wizard need to be dyno tested?

Joe

He is talking about emissions testing on the dyno where they need to see the mph for testing purposes. You need to get under the truck right near the t-case output and check to see if there is mechanical or electrical sending unit. Electrical would of course be wires and mechanical will be a thick cable like a bike shifter with a spinning cable inside it. The mechanical types use a removeable plastic gear and by counting the teeth on the gear you have you can do a little math and check to see if the gear tooth count you need is available from isuzu used on a different application (oem bigger tires). There is post around with some part numbers.

If you have an electrical speed sensor then you should be able to use the electric unit. the way they work is by chnaging the frequency of the signals sent to the ECM and add or subtract a ratio to make up for the tires. multiply by 1.123 for instance. In that case it shouln't matter what brand of vehicle they all work in similar fashion. Maybe you will have to pick the right wire off the sensor, dunno, the manufacturer might be able to help and more poking around the net.

Thanks Chris. Yes, the truck would be on a roller for inspection testing. They check the speedo. The vehicle cannot be traveling faster than the speedo reads or the vehicle fails until it is fixed.

I'll get under and check for the sensor or speedo gear. My previous truck had it on the tailshaft of the tcase. I imagine the Wizard will be similar, but I'll look at everything.

If it is electrically operated, I'm going to seriously think about wiring in a TruSpeed unit for another application. They all work on the same principle as you mentioned, they change the reading before it gets to the ECM. I don't see why it wouldn't work here.

Here is another option for you. There is a link to a review from someone who used it on a Cruiser.

How do the GPS units do for accruacy? Anyone know? I've got minor experience with GPS and it has been years. Without it using a land based, differential point for its calculations, I would assume the error rate would be rather signifigant. I guess it also depends upon on many satalites you are using to do the calcuation. ?!?

Michael

I got under the Wizard, it is electronically controlled.

Michael, thanks for the link to the Yellow box. I read the webpage and review and I think it is an option to keep in mind. For just over $100, that looks better than near $200 for a new TruSpeed unit.


I'm looking through the UBS manual I have here but I'm not real certain where to look for the ECM or box/harness where I'd connect. Is that going to be there under the hood? Eh, beans for now, I don't have the unit yet <img src="/forums/images/graemlins/wink.gif" alt="" />

Newer GPS systems based on the latest technology can acquire signals from more satellites and can thus achieve positional accuracy down to a few feet anywhere on the globe. Signal processing is such that higher vehicle speeds do not pose a problem, and even driving through tunnels is a minimal issue due to built-in compensation.

http://www.sema.org/main/semaorghome.aspx?id=52884

Joe