TBI VSS necessity

["Chris and Ranae Procyk" <procyk19@domain.elided>]

Hmmm, I have no doubt that you're correct for the later models, but I am as
sure as I am about anything -which is far from 100%.. you all are probably
figments of my imagination, when it comes to that-  that my 91 engine didn't
use the VSS for air/fuel mixture.

'Cause the engine sat for about 6 mos. as I studied the problem, as that
(the VSS) was the only thing I couldn't rig.  This was circa 1994,  maybe
previous to the aftermarket adjustment device you mentioned (were you saying
the GM VSS would just bolt onto a regular speedometer cable??)  and
certainly before I became an Internut- so I didn't have much choice.

I went forward and back thru GM's manual plus all the generic EFI manuals I
could find, and they simply didn't mention it, except in the GM manual in
reference to the t/c lockup.  At that includes sections that were very
similar to your excellent description of the MAP/Oxy/TPS functioniong.

It certainly doesn't miss it.  When you think about it, if you have throttle
position, pressure, and an oxygen sensor, n'nat, the actual vehicle speed
would be just icing on the cake, adding a very minor tweak.

In fact, I wouldn't be surprised if it's primary use was to cheat on the EPA
test!!

However, if you have some hard info that confirms that it was used by the
'91, I'd like to see it and the sources for the parts you mentioned.  I am
re-doing the entire vehicle soon, and I'd probably want to add the VSS in
any case.

BTW, is our ('91 on Vortec engines) distributor shaft the same as the
earlier GM HEIs?  In that case, we could certainly use the FAQ about
mounting a GM HEI to get the knock sensor working on an IH truck.  The
aftermarket knock sensor is like $400, and anyway, the computer may be
happier knowing the timing advance, although I suppose Turbo City et. al.
just patch any dependencies out.