[Gmecm] What does VSS do exactly?

[Charles McDowell]

Thanks for the reply.  I always thought the IAC "parked" itself when the car
was shut off.  Do I understand correctly that I will probably not have a
problem if my computer is the type that operates that way instead of
recalibrating above a certain speed? Is there any good way to tell which I
have? 

-----Original Message-----
From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On Behalf
Of WopOnTour
Sent: Saturday, June 25, 2005 1:53 PM
To: gmecm at diy-efi.org
Subject: Re: [Gmecm] What does VSS do exactly?

Charles
Depending on your box, VSS is used to trigger an IAC "reset" when a
combination of TP and VSS are above predetermined limits. (typically high
enough so the reset routine is not intrusive) At that time the ECM will
usually command 255 "in" counts and then back the pintle out to a
predetermined decel "ready" position (usually 60-140). It typically only
does this once per IGN cycle. This is necc as the IAC doesn't really have
any physical feedback circuit, so the ECM bases it's count strategy on this
reset position. On newer PFI units this reset occurs ay IGN off instead. So
not having a VSS may affect idle  performance since the ECM can't know
actual pintle position and can get quite a bit "out-of-sync" from the
predicted position posted up in the data stream and displayed on a scan
tool.
HTH
Regards
WopOnTour

----- Original Message -----
From: "Charles McDowell" <charles at taildragger.info>
To: "'For discussion of GM EFI hardware and software'" <gmecm at diy-efi.org>
Sent: Saturday, June 25, 2005 11:43 AM
Subject: [Gmecm] What does VSS do exactly?


>I converted my Blazer to TBI using a pre-made kit with no provision for 
>VSS.
> Everything seems fine, but I'm reading that I could have problems?  Can
> anyone say for sure what purpose the VSS serves?  I have all the emissions
> stuff disabled, so I don't care about that.  I've read some comments
> regarding IAC, but nobody can explain quite what that's all about.
>
> Thanks.
>
>
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> Gmecm at diy-efi.org
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