from a previous post
I was crusing and found this then saw your question - hope this helps.
service manual states: "With the engine running, the pump has 2 modes of operation: Mode 1: 100 percent duty-cycle with a minimum pressure of 10 psi except when the engine is cranking. Mode 2: 25 percent duty-cycle with minimum pressure of 7 psi with the engine cranking. The 25 percent duty-cycle is used to limit injection pump inlet pressure until the engine is running. " (2001 service manual, volume 2, page 14-79)My interpretation of this is that when the engine is running (other than cranking) the pump operates in Mode 1, so there should be no less than 10 psi with the engine running.