Cummins isx 2350 boost problems

[Lunchtime92]

Hey guys, I have a 2014 kenworth T800 with a cummins isx 2350. I put a brand new turbo on it a few weeks ago and noticed eversince that over 1500rpms I can't maintain boost pressure. It will still build 25-28psi of boost, but won't hold it. It will constantly fall back to 15-18 psi then build back to 25-28 then immediately fall back. It does this nonstop over 1500rpm. It hold 30-32 psi just fine under 1500rpm. Also the only fault codes im getting are spn 651, 652, 653, 654, 655 fmi 7. There is no audible skipping or misfire, so I changed the injector wiring harness. Faults still comeback within 20 miles of driving. Any help would be appreciated.

[Lunchtime92]

Found the culprit of this problem this morning, some one suggested to check the fuel return line at the back of the head for any kind of trash or gunk. When I took it off it was a little dirty but not terrible, but the check valve in the line was not functioning, it was staying open, so there was no back pressure. Put a new line and check valve on and that solved my maintaining boost pressure problem and the injector solenoid codes didn't come back all day.

[Rawze]

also do a rail leak-down test exactly like this video shows, and make sure it passes ...
ref: https://rawze.com/forums/showthread.php?...3#pid75483

[marek4792]

Did yours come with a sealing washer/oring? Looking to change mine as I experience something similar time to time without codes.

[Lunchtime92]

(08-31-2024 )marek4792 Wrote:  Did yours come with a sealing washer/oring? Looking to change mine as I experience something similar time to time without codes.

Yes it comes with all o rings