[Schrade]

Ok - I had (relatively sure hereof) a blocked OPEN check valve in the tank.

Test:

Both fuses in.

Power to test terminal.

Pinch feed line BEFORE rails inlet.

Power off test terminal. Pressure held @ 52.

Release pinch on rail feed inlet. Pressure dropped IMMEDIATELY ~12 to 40.*

Test again, NO PINCH, power off.

Pressure dropped VERY SLOWLY:
0:15 = 48
0:30 = 47
0:45 = 47
1:00 = 47
2:00 = 46
5:00 = 45

*This QUICK reverse flow MUST HAVE pushed SOMEthing [obstruction / sticking check valve] back OUT OF IN-TANK CHECK VALVE.

Could this be ANYthing else???????