[Gmecm] 93 CHEVY g20 VAN

[Gary Evans]

WopOnTour is correct on the reason for the vacuum referenced pressure 
regualtor.  On the TBI Subaru and Tracker, the vacuum line is plumbed 
in above the throttle plate. The purpose being (as said earlier) to 
maintain a constant pressure drop across the injector nozzle. In a TBI 
application, the only source of pressure drop at the injector is the 
air cleaner. In many designs this drop is ignored and is simply 
compensated by the computer. Other designs use a vacuum reference near 
the injector body to account for clogged air filter, etc.

That is the reason for the presence of a vacuum referenced regulator on 
some, but not all, TBI systems.




On Dec 31, 2005, at 12:56 PM, Ford, Pat wrote:

>  Strange, the tracker and cavalier both have vacuum lines, come to 
> think of it so does the tbi Subaru's.
>  From what I learned at trade school, Phil is %100, and that jives 
> with what I saw as a mechanic.
> Pat
>
> <-----Original Message-----
> <From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org]On
> <Behalf Of WopOnTour
> <Sent: Saturday, December 31, 2005 3:50 PM
> <To: gmecm at diy-efi.org
> <Subject: Re: [Gmecm] 93 CHEVY g20 VAN
> <
> <
> <Phil
> <There is no vacuum signal required on a TBI as the point of
> <injection is
> <always at atmospheric pressure.The vacuum line used on a PFI
> <engine IS NOT
> <to alter fuel pressure to compensate for load in any way shape
> <or form. It's
> <to maintain a consistent pressure drop across the point of
> <injection when
> <lower pressures (vacuum) exist. If there is 18" of vacuum at
> <idle, the fuel
> <pressure will be reduced an equivalent amount (approx 9 psi)
> <HTH
> <WopOnTour
> <----- Original Message -----
> <From: "Phillip Kuhn" <pmkls1 at yahoo.com>
> <To: <gmecm at diy-efi.org>
> <Sent: Saturday, December 31, 2005 10:13 AM
> <Subject: Re: [Gmecm] 93 CHEVY g20 VAN
> <
> <
> <> It is throttle body, they are pretty much ALL simple
> <> spring and diaphragm, and I'm still thinking they have
> <> a vaccum source wether it comes from inside the
> <> throttle body or has a separate vaccum line.
> <>
> <>
> <>
> <>
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