How do I figure VSS Ratio in the ECM Constants table in CATS Tuner? Can this be used to calibrate the speedo for rearend gear changes?

 

on a 3rdgen, the VSS is a set number of pulses per mile.

to calibrate for rear end changes, you swap plastic gears in the trans.. just like cable driven speedos.

 

Or you can buy a unit that adjusts the pulses from Dakota Digital..
http://www.dakotadigital.com/Detail....-5/product.htm

 

92BLKL98, the preferred way is what MrDude_1 said, you can also go with what Cliff92Z said, both will work.

i don't know about CATS, but with TunerPro RT with a 730 ECM running the AUJP bin with either 8d_v03 or Super_8dm2 ECU files, i know there you can make changes to alter the speed reading in the ECM.

the 8d_v03 ECU file is easier to set it with because it uses
0 - 255 for the setting where Super_8dm2 uses pulses per mile & when you change the pulse per mile enough the accept the
change, it changes by 1 number in 8d_v03.

as to how to calculate how much & which way to change it, i have no ideal, that would involve math & for me it was easier to run it on the dyno using real time emulation & my lap top.

 

Why not just change the PPM, and speedo correction ?

-- Joe