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Re: VSS question



There are a few things in the code that look at vss.  Mainly if your moving
or not, doesn't matter how fast.  Off the top of my head, fan controls, fans
shut off at 35 mph, also idle stuff as you have found out.  If the engine
speed goes below a certain rpm then the ecm goes faster to make sure the
vehicle doesn't stall.  There are probably more.  DFCO, declleration fuel
cut off. ect.
Hook up a vss.
Mark
-----Original Message-----
From: Andrew Choset <agc3@cornell.edu>
To: gmecm@efi332.eng.ohio-state.edu <gmecm@efi332.eng.ohio-state.edu>
Date: Tuesday, January 18, 2000 6:39 PM
Subject: VSS question


>In a manual transmission car with a cable driven speedo, and no cruise, is
>there any real purpose for the VSS?
>
>Background to my question--
>
>88 IROC-Z, L98, originally 700R4 with cable speedo.  Swapped in T56,
>replaced speedo with AutoMeter electric speedo.  Stock speedo incorporated
>an IR pulse generator to feed a signal to the VSS buffer box.  As it sits
>now, there is no pulse generator, and the VSS buffer box gets no signal,
>therefore the ECM gets no VSS signal.  As a result, code 24 would set.  OK,
>use a jumper to close the Park/Neutral switch, to fool the ECM into
>believing that the 700R4 that no longer existed was always in park, and
>therefore the ECM didn't look for any VSS input. Did the trick, no more
>code 24.
>
>However, it soon became apparent that I've got an idle issue... upon coming
>to a stop (trans in neutral), the idle speed will often hang out around
>1500rpm, sometimes even a little higher.  Is there a possibility that this
>is a result of not having a VSS input?  The problem does *not* occur
>always, in fact, sometimes I'll go a week without having the problem.
>
>Any ideas?
>
>Thanks in advance.
>
>Andrew Choset
>
>