ISX cm2350 low. power/poor. Fuel milage.

[JimT]

Just reread your original post. The air compressor intake is probably not leaking, IF your pressure test included that section, but probably worth checking for signs of wear as it's hidden internally.

Another thing that you need to look at is the fuel pump and rail. The cm2350 has the famous high pressure pumps that are known to go bad after about 400k miles or so. Insite can monitor fuel pressure commanded and measured and of course watch for fault codes, though problems can be present for a while before actually triggering a fault.

Small fuel rail leaks can also create a whistling sound. Following the procedures on Quickserv carefully check all the connections and torque to specs, including the one going to the doser injector on the turbo. The rail pressure relief valve is another thing to check.