You both have a good point. Volume/Pressure at speed would be the critical test. What rags me is that the giganto enourmous tank still has 15 or more gallons in it when the prob occurs. It seems that there should be plenty of fuel to pick up - no cavitating or slosh problems should occur at that level although if a small air leak would occur it should also present some bubbles in the fuel rail. One screwy thing about the oddball geegaw that holds the pump requires a substantial level of fuel before it enters the pump ‘chamber’. There is no pickup tube just this chamber where the pump sumps the fuel up thru a screen. Stupidest design I could imagine. I was told you never want to run one out of fuel.
Now that I think of it though the old pumps would shoot a good full (unrestricted) stream 15-20 feet when testing. As I stated they make a good parts washer pump.
I thought for some time of replacing the entire p.o.s. with an external pump but a mechanic freind told me of the Ford rollover probs in the early days of these high pressure systems when the pump kept running and caused hellish fires. So I changed my mind!
Thanks for the info.