Stray vacuum line

alan cordeiro alancordeiro at
Sat May 21 11:31:50 EDT 2005

The wastegate spring provides just enough force to keep the wastegate
from popping open to 1.4 bar.  If the ECU does not "intervene",
this is where your boost will end.

If the ECU perceives the requirement for more boost, it turns on
the WGFV solenoid, which begins to bleed of some of the excess
pressure below the wastegate diaphragm, decreasing the upwards force
on the wastegate (i.e. raising the allowable boost).

(Note, older designs used to ADD manifold pressure at the top)

If you look at the boost vs rpm curve, the ECU starts
trimming down the boost after 4000 rpm to keep the
turbine from spinning past its maximum allowable rpm
( is this 150,000 or 200,000 rpm?) and self-destructing.


----- Original Message ----- 
From: "Michael Sylvester" <msylvester at>
To: <turborotary at>
Cc: <200q20v at>
Sent: Friday, May 20, 2005 10:10 PM
Subject: Stray vacuum line

The spring alone will allow only 1.4bar.
To get greater than 1.4bar the ECU needs to pulse the WGFV.
If the spring were set to allow 1.8 bar of boost, you would certainly
destroy the engine in short order.

Mike Sylvester

Thanks for the response, the end of the hose is cracked, so it makes
sense that the heat caused it to deteriorate and fall off the bypass
valve.Though, if the wastegate frequency valve is bypassed, shouldn't
the wastegate only open when the boost equals whatever the internal
spring is set to (which I assume is 1.8 bar?)
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