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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
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Originally Posted by gsmith660 View Post
I am going to take everything off from the throttle body and get rid of the AAV for now and check it all but is it normal for the side of the diaphragm that has boost on it to not hold a vac
That diaphram in the WG hooks to the valve stem, pulling it off it's seat (against the WG spring tension) when the diaphram is pressurized by the boost signal. The valve runs through a guide, and it's the guide that will allow some air to pass by it. So if you're applying vacuum to the boost port on the WG, you won't be able to hold it due to the air coming in through the guide.

It's not such an issue when you're applying oodles of boost air volume...that small amount of leak-by isn't a concern until the guide wears badly enough to where you can't sustain pressure in the diaphram, resulting in the WG not opening quick enough and creating boost spike issues....the reverse of the symptoms you're experiencing.

Probably a poor description, but something like that anyway.
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 05-01-2013, 02:04 PM
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