Hi, I haven't read the full thread but thought I'd add a couple of notes. The fuel rail should hold fuel pressure while the engine is running. Thats what the regs job is. I have a Sard rising rate reg set for 40PSI (thats what I see on the fuel pressure gauge when idling) and when under boost the reg lifts the fuel pressure 1 PSI for every 1 PSI boost. If I turn the engine off it holds the 40 PSI in the fuel rail because I'm using a one way valve in the fuel feed line. Some pumps have one way valves and others don't. I think my Walbro does but I also have an inline also. This stops fuel bleeding back through the fuel pump when the engine is off. I can leave the car for weeks and still see the fuel pressure gauge showing 30+ PSI. I'm guessing it does leak down a little and as temps come out of the cooling engine and sitting around. Hope that's of help.