How much boost while jaking 871

[Rawze]

Ours gets up to about 18~ish psi (cm871) on its highest setting at around 1400 - 1500 or so.

One possibility is weak electrical connection to the jake solenoids. The plug going into the head and/or the slip-on connector at the solenoid sometimes makes weak contact.

Exhaust manifold and/or egr circuit leaks will lead to weakened turbo response and weakened jakes too. One culprit that gets overlooked is the pipe (pipe that has the egr temp sensor) that feeds between the egr valve and the venturi on the intake side of the CM871. They like to separate right where it meets the top of the egr valve. A hard yank on it where it goes down to the top of the egr valve will reveal if its connection is bad.

It can also be a turbo that is loosing proper calibration or hanging up at higher positions like others have said. If there are not any exhaust manifold or egr circuit leaks, then one easy test would be to manually command it to 95%+ closed at idle to see if it chokes the engine. If it can't then taking it apart and checking if the VG ring hangs up at higher positions, or there is excess play in the sector gear on the actuator is the next step.

https://youtu.be/ZUpKb5umv_0