X15 2250SN fault code 1911

[Kenworth509]

Hey guys I’ve got a X15 2250SN with a fault code 1911, engine is no deleted or any modifications with calterm.
I’ve done extensive testing of fuel components and still no luck, the rail pressure fluctuates at idle from 9500psi-5900psi while command pressure is 7200psi. Once you shut it off it will maintain rail pressure but it’s up from anywhere from 8500psi to 10500psi while command is still 7200psi.
When driving in high rpm the rail pressure gets to 42000psi and you back off the throttle and the rail will just hold that high pressure anywhere between 27000psi to 42000psi while command is right down around 7200psi
I’ve inspected all fuel pump components and even ran another fuel pump head and actuator and still faults, no air is present in the system when hot or cold, replaced rail pressure sensor, rail relief valve.
I’ve done a fuel pump performance test all ok at 175ml over 30 seconds cranking at 130rpm.
I’ve done an injector return flow test and over the 60 seconds only 40ml is measured. Quickserve only list a maximum injector return flow and nothing about minimum.
It also passed an injector performance test but I’m starting to think there is an issue with the injectors possibly.
I’ve also swapped ECMs and tried different cummins calibrations just to cancel out the electrical side of things, engine harness is fine as well with pin out testing all ok.

If anyone has any handy info or can help let me know Thankyou.