The fpr watches manifold vacuum, and raises fuel pressure at low manifold vacuum. I get that high vac means light throttle/cruise conditions, and low vacuum means more throttle, needing more fuel. But changing the fuel pressure doesn't make sense to me. The injectors will flow more of course, but the tuning data changes at the same time. So the ecm has to juggle pulse width with the changing pressure. Why not just leave fuel pressure constant, say 50 psi? What is the point of reduced pressure at cruise? To save wear on the fuel pump?