Good afternoon and welcome to JustAnswer!!
My name is ***** ***** I have worked for a Chrysler-Dodge-Jeep dealership for 19 years and I will do my best to help.
I have been working on Cummins engines for 20 years at the dealership and you have done some good testing, but something doesn't add up.. The cause of your no start is the low rail psi which you have found and the causes would be leaking injectors/transfer tubes, or a bad PLV. When the fuel leaves the CP3 it goes directly to the common rail and then to the injectors. Either one or more of the injectors are leaking or you have a bad PLV. You have already replaced the PLV and had the injectors rebuilt so the pressure has to be bleeding off somewhere, but this is where it gets tricky. You have unplugged the FCA and caused the CP3 to build MAX psi which is 26,600 and it did so but did you disconnect the FCA and try to start it? Did it start then? Also there is a bulletin that says to check the return line to the tank as it could affect the CP3 and cause a no start.. Here is the bulletin..
Vehicle Issue No start. The truck is being repaired after fuel system contamination.;The transfer (lift) pump, high pressure pump, and injectors have been replaced. The engine still will not start.
System or Component No Start;DTC / Error Message;Group 14 - Fuel System,Fuel Pump / Transfer Pump,Injection Pump,Injectors;Recent Repairs;Yes - Intermittent,Yes - Continuously
Recommendation Inspect the complete fuel return system for a restriction or blockage. There could be debris from the contaminated fuel lodged in the return system which effects the high pressure pump operation.
Let me know your findings,