ScanMaster MPH

[zeus87gn]

I have had my ScanMaster for over a week now and have already figured out a couple of things that have allowed me to make this poor old machine run soooo much better. I have definetely been missing out without it. Certainly worth the money.

Question for those that know:
Is the MPH reading correct regardless of tire size?

I ask because our GN has the original rear, I run 255/60's, and we are on our third transmission with unknown gears. If memory serves, the signal to the computer comes from the speedometer cable sensor which is run off the tailshaft of the trani. The trani gears should not matter, it's the rear final ratio that mattters. With 255's and the stock 3.42, I am supposed to be 4% slow. My ScanMaster reads the same as my speedometer.

Are they both wrong because of this or has my speedo gear been adjusted for tire size and they are both correct? Latest trani was installed just before it came into my life.

Thanks for the help.

 

[TurboDave]

I have had my ScanMaster for over a week now and have already figured out a couple of things that have allowed me to make this poor old machine run soooo much better. I have definetely been missing out without it. Certainly worth the money.

Question for those that know:
Is the MPH reading correct regardless of tire size?

I ask because our GN has the original rear, I run 255/60's, and we are on our third transmission with unknown gears. If memory serves, the signal to the computer comes from the speedometer cable sensor which is run off the tailshaft of the trani. The trani gears should not matter, it's the rear final ratio that mattters. With 255's and the stock 3.42, I am supposed to be 4% slow. My ScanMaster reads the same as my speedometer.

Are they both wrong because of this or has my speedo gear been adjusted for tire size and they are both correct? Latest trani was installed just before it came into my life.

Thanks for the help.

The scanmaster WILL read the same as the speedometer. The speedo sends it's info to the ECM. The scanmaster gets it's info from the from the ECM.

 

[garyk1970]

what dave said and, behind/coming out of the cluster is the vss box(green) it gets its readings from the speedo and sends the speed to the ecm,then to the scanmaster,so its going to read what the speedo "sees" even if its wrong.

 

[zeus87gn]

Figures...

 

[bison]

Figures...

PM me your exact tire height and i can figure out the combo of driven and drive gears in the trans to get your speedometer and odometer very close. Stock uses 11 (orange gear) drive and 30 driven (blue gear).

 

[bison]

According to my calculations with 255/60-15 (27 inches tall), 3.42 rear , and the stock 11 tooth drive gear all you need to do is get a 28 tooth (yellow) driven gear. Its about a 10 minute swap out by pulling the speedo bullet out of the side of the trans. This will get your speedo and odometer very close.