Ok, I connected a fuel pressure tester to my fuel rail today to check out the effects of connecting the fpr vac pipe to the manifold. MarkV is spot on about the way the regulator works, the vacume reduces the fuel pressure.
Connected to the manifold I got 3.2 bar fuel pressure on idel, (i.e. when you see max vacume). BUT....As you rev it (and vacume in the manifold is reduced) the fuel pressure moves up to nearly 4bar. However, overrun when the throttle closes completely the fuel pressure is down to 3 bar.
So as you can see the FPR connected this way is working how I understand you would want it too? Low pressure at idel and high pressure under WOT.
Now the question is if the ECU is programmed to operate under a variable fuel pressure or not because my understanding of the way its conected as standard with virtually no vacume would mean it used to be static at 4bar? Will the ECU be all over the place with the fuel trims if its not set up to deal with variable pressure.
Anyway.....heres a quicktime video of the fuel pressure moving with revs. Im sorry its not that great and only shows the pressure moving to 4bar once at the very begining of the clip when Ian gave it a good rev but you can clearly see how its working.
http://homepage.ntlworld.com/w.marsland1/MOV00248.MP4