DJD, 4psi is way low. Sounds like the lift pump is gone and it took the injection pump with it, which is not uncommon (as PHX ATC said). I can get you a deal on the parts if you need a VP44. The best deal on the lift pump is direct from Cummins, around $140. PM me if you want a price on the VP44.
If you are ever going to change the lift pump don't even bother going with a stocker. At the very least buy a carter 4601 pump and relocate it at the take, which would make the system a push not a pull(which is best). If you want a nice system spend a little money and buy a FASS sysem www.dieselpp.com there is nothing better. I have one on my truck, with injectors, and an edge comp at wide open I have never seen below 15 psi of fuel, idle at about 20. The FASS has ,I think, a 600,000 mile warranty. The only reason that you will ever have to replace a Injector pump is fuel. Whether it running it out of fuel, not enough fuel(lift pump bad), or bad fuel. Other than that they will last.