04 ISX CM870 boost issue

We have an ISX 400 CM870 in a 04 W900B. Lately we've been having some boost issues. The truck will pull 30psi of boost for awhile and then under load, on the throttle, not on the throttle, it doesn't seem to matter it will only go up to 20psi of boost and that's it. If you are on the throttle when it occurs it's like a switch is flipped and bam it will drop from 30 to 20 in an instant and the most you will ever see again is maybe a spike to 22.5. It will still hit 27psi on the stage 3 jake though when this problem is occuring.

What we also found out today is that when we can only pull 20psi of boost, if you turn the key off and then back on again... even quick enough where you don't have to restart the motor, it's like something will reset and we can make 30psi of boost again for awhile.

Any ideas? EGR?

There is no CEL occuring at all.

Thanks.

 

That's what we were kind of thinking as well. Hopefully will be hooking it up to Cummins Insite this weekend to do some troubleshooting/data logging.

Appreciate the reply!