I am using Tunerpro v5 with $8d mask on a 7730 ecm with s_aujp_v41026 bin. I just finished a T56 swap and have an Autometer electronic programmable speedo. Calibrating the speedometer is fairly simple but my question is how do I tell the ecm how fast the vehicle is going? I noticed a vss pulses scalar at hex address 0x15 in Tunerpro and I'm pretty sure that needs to be changed however I'm not sure how many ppm the T56 vss is. I did a search and all I could find was the vss puts out 17 pulses per revolution. How is that converted to pulse per mile with 26" tire and 3.73 gears?

 

if 17 PPR is correct....

17 * 3.73 = 63.41
26" tire makes 775.58 revolutions per mile.
63.41 * 775.58

=

49,179.5 pulses per mile.

 

Thanks for the response Saar. So basically I change the scalar to 49,179.5 ppm or something close to it and the ecm will be happy?

 

correct. that will give the ECM the correct value to work with to create an accurate MPH value. since you're not using the 4K PPM signal from the ECM for the speedo, then you don't need to mess with the divisor stuff either.

 

Awesome stuff thx saar. I have an sgi 5b box but didnt feel like running additional wiring.

 

should you decide to swap tire sizes or the diff, i use this calculator all the time.

http://www.discounttiredirect.com/di...foTireMath.jsp

just multiply PPR by diff ratio by revolutions per mile.

 

Great stuff thx again!

 

Quick update, I finally got around to calibrating the Autometer speedo and ECM. The Autometer ended up reading 48,878 ppm. I changed the vss scalar to the closest number which was 48,505ppm. ECM, GPS, and speedo are all dead on