Setting up $A1 for OPTICAL VSS

[Mars]

Anyone know how to do it ?

It's easy using Code59, it's just a flag you set in tunerpro, then you use pin C6 on the computer for VSS, but none of the def. files I have for $A1 have that flag...

I know this is an easy fix for you experts.

Can paypal anyone some $$ to get me the fix. Thanks.

[robertisaar]

technically, there is no flag in A1 for it. or at least, GM didn't indicate one.

however, try setting 0057 bit 4, this is the equivalent bit that worked for getting optical VSS on $88 working.

keep in mind that byte also controls the 4K PPM pulse divisor, so if you change that after setting the bit, you'll have to re-set it.

[Mars]

ok cool thanks.

if that don't work, i'll just go code59. im sure it will be fine for NA tunning as well.

[Superdave]

As long as that VSS I showed you works with your transfer case, you shouldn't have any issues using the standard input.


I know Robert and I talked about this when I was dealing with it on my Camaro. I know I tried that other VSS input pin but i don't remember if I changed anything in the code.

[robertisaar]

i know that the older masks that were intended to be used with an optical input as an option have a filtering routine that isn't present on 88/A1/later, i don't know how critical it is using an optical signal with magnetic code, but it wouldn't surprise me if there were a small amount of jitter in the signal. i haven't looked at it in a while, but i'm almost certain there is filtering done on the magnetic signal as well, just not as significant. there might be a filtering coefficient to play with to correct for it if it bothered someone enough.

[Canyonero]

I'm running hall/optical VSS (integral to the Isuzu cable-driven speedometer) with a '7727/$88 as per robertisaar's instructions. I'm not sure of the technical aspects, but changing the bit and connecting the VSS to the optical input pin worked for me.

There is a ratio converter somewhere on the truck that dropped the speedo's 4k ppm output down to 2k ppm for the original '8062 TBI ECU. I'm not sure where that converter actually is, so I simply adjusted the input down to 2k ppm in my $88 bin. The Isuzu 4cyl ECU and the cruise control module take 4k ppm, so that ratio converter is not installed on the 4cyl vehicles.