[s-cars] While we are on the subject of WGFVs...

[Theodore Chen]

dave,

just want to make sure we're on the same page here.

we agree that in order to increase boost, the ECU actuates
the WGFV to reduce pressure in the WGFV-WG hose.

if i understand you right, you're contending that rather
than just bleeding off boost, actuating the WGFV causes
a vacuum to be created in the WGFV-WG hose, which helps
to hold the wastegate shut.

in other words, rather than just reduced positive pressure,
you're saying there is negative pressure in the WGFV-WG
hose when the WGFV is actuated.

i have no opinion on that point, and i don't disagree with
you.

you said:
"If the ECU decides that all conditions are good for high boost operation, the
WGFV allows the vacuum source to pass through it to the WG, and this
effectively increases the WG's ability to remain closed.  Net result... the WG
remains closed to a higher boost level than would be attainable with the spring
alone."

agreed.
 
"If the ECU decides that conditions are not good for high boost operation, the
WGFV begins to cycle the boost port open, allowing boost to pass through it to
the WG, and this effectively decreases the WG's ability to remain closed.  Net
result... the WG remains closed to a lower boost level than would be attainable
with the spring alone."

my understanding is that the boost port of the WGFV is always
open, and so is the wastegate port.  the only port being
controlled by the WGFV is the intake port, which is normally
closed.  when the WGFV is actuated, the intake port opens and
is connected to the other two ports.  i verified this by 
testing with a 12v source and blowing through the ports.

i would describe it thusly:
"If the ECU decides that conditions are not good for high boost operation, the
ECU begins to reduce the duty cycle of the WGFV,
cycling the vacuum port closed, reducing the vacuum and 
increasing boost passed through it to the WG, and this effectively decreases
the WG's ability to remain closed.  Net result... the WG remains closed to a
lower boost level than would be attainable with the spring alone."

would you agree to that?

this is an important point, because your earlier phrasing
implies that actuating the WGFV (increasing its duty cycle)
reduces the wastegate's ability to remain closed (and thus
causes the wastegate to open).  i believe that increasing
the duty cycle of the WGFV increases the wastegate's ability
to remain closed, and this is consistent with your later
observation that unplugging the WGFV (reducing its duty cycle
to zero) causes the wastegate to open at low boost.

sorry for belaboring this point, but it is more than academic
to me because i have been trying (off and on) to fix this 
freakin' car for some time.

-teddy

--- Djdawson2 at aol.com wrote:

> In a message dated 1/11/2006 6:42:23 PM Mountain Standard Time,  
> tmullane at gmail.com writes:
> 
> Teddy is  correct.  Unplugged, or without voltage from the ECU, the
> WGFV allows  boost through to the WG, opening it.
>  
> I agree, and stated that in my response to Teddy.  Yep, default  mode... if 
> something isn't working right, the ECU (and the mechanical design)  default
> to 
> a setup that allows very little boost. 
>  
> 
> When voltage is applied, the valve opens the third port, allowing boost to  
> both the WG and into the intake boot.  This bleeds enough pressure off so 
> that 
> the
> WG does not open.
> 
> 
> 
> So, are you suggesting that "bleeding off pressure" is the only way the WG  
> remains shut?  If that is the case, you're suggesting that the WG spring, 
> and 
> only the spring, is responsible for holding the WG shut.  That being  the 
> case, how would you explain the fact that we are capable of running higher 
> boost 
> levels than the spring alone (no WGFV or ECU input allowed) can  maintain?
>  
> Yeah, Mark is right... this has been beaten to death.  But I'm not  quite 
> sure how anyone makes the logical leap between a WG spring that will only 
> allow 
> 14 or so psi by itself... and the fact that we can run double that with  the 
> WGFV functioning as designed.
>  
> The ONLY way the spring can be assisted, from the bottom of the WG  diaphragm
> 
> to allow more boost than the spring alone, is by introducing a  vacuum.  That
> 
> is simple fact.
>  
> Dave (and I'm smiling about this age old topic)
> 


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