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BPV's on 9-5's, closed at idle!
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Posted by Dean (more from Dean) on Sun, 31 Aug 2003 13:00:17 Share Post by Email
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I read some stuff on BPV tunning, shimming washers etc, suggesting that there would be better performance if the BPV was not wide open at idle and to shim so that is was not open or not open very much. OK, something that I can check out...

So I put a bosch back in place and put the vac line on the TurboXS BPV which is now off to one side. Intent is to see how open it is with manifold vac at cold and hot and perhaps install some shimming washers.

Nope, the BPV does not open at all. There is no VAC at idle. Actually very weak positive pressure at idle when cold that goes to almost zero pressure when hot. Why? The vac goes to an ECU controlled valve that controls what the BPV does, independant of manfold vac or the vac at a port in the TB.

So all of the thinking about how these things act as part of a passive response type things is out the window. The ECU controls the BPV. So why? I hope that someone else can explain. One benefit is that the bosch valve diaphragm does not get stressed all the time that one is at part throttle. That is an improvement. The boost should also come on fast this way I expect.

The BPV can be controlled by the ECU via the TPS and/or the MAP signals depending on what the software does.

So the TurboXS BPV is back in as it was, no shimming washers installed. I think that one should not shim BPV springs in adjustable units. Leave such out and the ECU manage things. With the shiming washers out the valve will open wider and faster. Boost pressure via the VAC lines will hold it shut by balacing out pressures that want to open the valve. The spring pressure will hold it closed with the pressures balanced.

posted by 65.68.102...
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