Isx15 2250 engine brake issue

[Rawze]

(05-23-2026 )Samvelm83 Wrote:  ...
Can it be from the jake brake check valve or the spring ?

It can as well ... but you said you already replaced them in post #3 above. Those components are internal to the jake solenoid units on a CM2250.

It can also be worn out rocker shafts letting too much oil past them as the oil gets thinner. This can be checked by pulling the valve cover off it and running the engine without valve cover, and then manually activating jake solenoids one at a time and watching for excessive oil flow from places where it should not be.

I would do the injector leak tests first though, as mentioned above, because it does not involve taking anything apart unless there are issues.