BPV was: CEL possible O2 sensor 1.6 bar now 1.3 SOLVED?

C1J1Miller at aol.com C1J1Miller at aol.com
Tue Sep 7 20:37:20 EDT 2004

In a message dated 9/7/04 6:56:25 PM Eastern Daylight Time,  
200q20v-request at audifans.com writes:

Quite a  bit of surprise on the Bosch BPV's leaking (hissssssssssssssssssss) 
at 8  PSI.  The concensus is that the turbo is just working harder to build 
maintain boost.  Time for another brand?

Q:  We had a  debate on which way the orientation of the BPV should go.  I 
know  there is a right and wrong direction. But in testing the valve we found 
pulling vacuum against it (side port) yielded slightly higher numbers than  
the (presummed) correct orientation when we removed  it.

Scott Mockry's site has a picture showing proper installation:
Check the small fitting to see if it holds vacuum, yes.  That's what  opens 
the valve; the partial vacuum after a closed throttle body...
In boost conditions, the small fitting supplies boost pressure from the  
intake manifold to one side of the diaphram, while the turbo hose provides boost  
pressure to the other side of the diaphram.  Spring pressure should be fine  
to hold the valve shut since there is equal pressure (boost) on each side.   
Actually, the area on the side with the small fitting is likely larger, making  
it even easier to stay closed under boost conditions.  Under very high  boost, 
this kind of valve may leak because the sealing diaphram is only  reinforced 
around the center, and some flutter during rapid boost change may  cause 
leakage or tearing.  Probably more of an issue with intake manifold  design and 
intake path length than anything else...

Chris  Miller, Bolton MA USA, c1j1miller at aol.com
'91 200q20v ==>  http://members.aol.com/c1j1miller/index.html

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