Originally Posted by J Wikoff
L67'* that unhook the BCS get normal bypass operation as far as creating boost is concerned. The BCS introduces boost pressure to the lower half of the BCA to close the valve.
The way you have it is an unknown, as far as I'm concerned.
Ok, did some playing with a vac pump and the valve. Here'* what I'm seeing:
Vac applied to the top chamber opens the valve, released the springs close it.
Vac applied to the lower chamber locks the valve closed.
Vac applied to both also leaves the valve closed.
Positive pressure applied to the lower chamber Opens the valve.
When the boost control solenoid is off, it is connecting the lower chamber to the lower intake manifold.
When the boost control solenoid is on, it is connecting the lower chamber to outside air through the foam filter on the end of it.
So, based on that, the only thing the ECM can command the valve to do is open (by turning it off electrically), provided it the lower intake manifold has a positive pressure. In other words, it can only dump the excess boost pressure from the lower intake manifold back into the plenum to recycle it back through the blower. Correct?
That said, connecting the upper chamber to the upper intake manifold is in effect trying the valve to the throttle plate. (Valve stays open in all states except WOT when the plenum vac goes away?)