Lost my IDLE boost

[Rockwell]

2011 MP8 445 with 650K miles

The Normal:
Every morning for the past 5 years of ownership, I turn the key on, wait for GuardDog to complete its check, and start the motor. The motor runs very quietly, and in 4 - 8 minutes or so my turbo would spool up to about 5 or 6lbs and decrease to 2 or 3 and the sound would become a little more gnarly accompanied by a very distinct, steady whistle of the turbo. At this point on cold mornings white vapor would then start coming out of the stack.

This was always my “signal” that she was about ready for work.

The Abnormal:
Suddenly, now when I start the truck, the motor stays in its first stage of “quiet” running, the turbo does not spool up, the gnarly sounding idle does not appear and not a hint of white vapor from the stack.

The truck runs fine, pulls fine, makes about 34 lbs max boost but it now idles at 1lb. Before this, it always idled at 2-3 lbs of boost with a very distinctive turbo whine.

There is no boost leak that I can find with just my hands and ears, CAC, boots, pipes all look good. Intake manifold gasket and bolts were all replaced 2 years ago and looks fine, no broken bolts.

There is a “rushing air” noise near or at the EGR, this noise will suddenly stop and boom, I hear the turbo come to life, however I can find no leak, Truck has always had this noise, has even fooled mechanics into thinking there was an air leak. Keep in mind, this is all at idle.

Any ideas?

[JoeH]

DEF causes turbo to spool. Not familiar with Mack emissions trucks though. Don't know when DEF started...

[Mack Technician]

You still on your first Turbo?

I’d pressure check the CMCAC system with engine off and then run it till the rack and pinion actuator for the turbo nozzle ring gives up some top end performance or kicks a code. 

Edited December 30, 2019 by Mack Technician