[Gmecm] Re: TBI 350

[Steve Ravet]

> -----Original Message-----
> From: gmecm-bounces at diy-efi.org 
> [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Jared Ryan
> Sent: Thursday, July 13, 2006 12:11 AM
> To: gmecm at diy-efi.org
> Subject: Re: [Gmecm] Re: TBI 350
> 
> 
> The more I think about it, the more I wonder if this engine 
> would really benefit from the vacuum-controlled regulator.  
> The issue seems to be that if I raise the pressure enough 
> that it doesn't ping on acceleration, it doesn't idle very 
> well at all.  The vacuum-controlled regulator would seem to 
> address that very issue.

The vacuum regulator is meant to keep a constant pressure across a port
style injector, so that a given pulse width flows the same amount of
fuel under all manifold conditions.  This is because the nozzle of a
port style injector is exposed to manifold air pressure.  The change in
vacuum from 18 inHg at idle to 0 at WOT is a change of 9 psi across the
injector.  With a vacuum referenced regulator the injector always sees a
constant pressure from inlet to outlet, and therefore always flows a
consistent amount of fuel.

Your TBI injector isn't exposed to vacuum, it's exposed to ambient air,
therefore it needs a constant input pressure.  The calculations and
tables inside the ECM assume that the injector flow is proportional to
pulsewidth, not also proportional to MAP or other factors.  You can add
a vacuum referenced regulator but in the long run when everything is
running right you will have ended up tuning out the effect of the rising
rate regulator in your VE tables.


> I have ordered a fuel pressure gauge with Schraeder-valve 
> adapter and paid for next-day-air shipping, so hopefully by 
> Saturday I will be able to report exactly what the fuel 
> pressure is at idle and at wide-open throttle.

Good.  Until you've done some diagnostic work, the speculation is just
farting into the wind.

--steve


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