CM2250 Leaking Injectors

[shouldvekeptmy379]

I am working on a CM2250 500HP, stock emissions, CPL 3491. Its having an issue with dropping fuel rail pressure 29K to 300psi in less then 30 secs. Fuel pressure release valve is brand new and tested. Fuel pump head has been replaced with metal internals but was done before customer bought truck, Ive had the head/plungers apart for inspection and they are good and in spec. Truck has 495K for mileage.

I have performed the High-pressure fuel leak test with insite. The pressure relief valve return flow was in spec. Injector return flow was in spec, 150ml in 60 secs(all 6 still hooked up, none blocked off). Fuel pump return flow was 310ml in 30 seconds, so in spec. I went ahead and blocked each injector off anyways one at a time thinking maybe one was leaking down somewhere else other then return flow. What I found was that if I block off #2, system would hold to 7500psi rail pressure at 30 seconds. If I blocked off #4, system would hold to 6800psi at 30 second. If I blocked off #2 & #4, system would hold 28500psi at 5 minutes. My question, is there a way to test (to confirm) injectors leaking into the combustion chamber? Coolant system looks, smells, and taste good. Most of the time I see leaking injectors they show on the return flow test.

This truck also builds 43psi(yes I know a lot) of boost( I haven't been given the opportunity to go thru egr system), has the following codes, 3135, 3375, 2754(one count each) and 0778(63 count), 2322(72 count). Cam sensor and crankshaft are new from Cummins so leaning towards wiring issue but this issue wasn't priority of customer as the cam sensor codes haven't derated truck.

Truck has the most current ecm configuration(that I could find) I believe CL10053.46 looking back at my notes.