Good comments, John. My analysis may be totally wrong. Here's some of my observations.
The crankcase vacuum with a properly operating CCV is reported to be 3 to 6 inches of water at idle. I measured the vacuum at one of the intake manifold nipples at 20 inches of mercury at idle. That's a lot of difference in vacuum.
Hose #3 connects the upper part of the CCV (the actual valve) to the vacuum of the intake manifold. Hoses #2 and #4 connect the lower part of the CCV (the oil separator) to the crankcase. That nipple to which the vacuum tube going to the FPR connects is below the diaphragm in the CCV. So my assumption is that the vacuum supplied to the FPR follows the operation of the diaphragm.
I agree that the every FPR I've seen operates by lowering fuel pressure as the vacuum supplied becomes more negative.
But it's also a fact that PCV valves have reduced flow at idle and higher flow at open throttle conditions. The top part of the CCV is essentially a PCV valve.
There appears to be ample vacuum to suck the oil out of the crankcase if the lower part of the CCV operates at intake manifold pressure. So the question is how is the intake manifold vacuum supplied to the FPR through the nipple on the CCV without creating so much vacuum in the oil separtator that the oil is pulled into the manifold?
EDIT: BTW, can you tell if the vacuum hose attached to the large vacuum port on the back of the manifold goes to the brake booster or the sucking jet pump?
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Last edited by Steve530; 01-20-2012 at 10:16 PM.