[Gmecm] What does VSS do exactly?

[WopOnTour]

Well it can be done by observing a noid light or the IAC (valve removed) 
when the IGN is turned OFF. BUT BUT BUT, if you have removed the IAC, you 
MUST physically limit the travel of the pintle so it doesn't go shooting 
across the shop. If it extends and then retracts after the IGN is shut off, 
you should be OK. But if it stays in position when the ECM is powered down, 
then it will need VSS input to help trigger the reset.
JME
WOT
----- Original Message ----- 
From: "Charles McDowell" <charles at taildragger.info>
To: <gmecm at diy-efi.org>
Sent: Sunday, June 26, 2005 12:49 PM
Subject: RE: [Gmecm] What does VSS do exactly?


> 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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