Loosing air pressure when engine is running.

Or it's not.

 

I had a 2006 Century with the MBE4000 engine, had an air line come off the bottom of the turbo, think it actuated the variable vanes or something like that. It lost a lot of air while running, zero air loss when shut off, but with the air line off it made so much noise that I was able to track it down. Not at all the same engine as the DD15, but they are both designed by Daimler-Benz.

The ultrasonic leak detector can be used on a running engine, but it takes some practice to get use to the sounds that you are looking for.

 

Check the fan hub I had the same thing on mine couple years ago.

 

just lots of little plastic parts, always breaking = always in stock

 

And always replacing… at the worst possible time.

 

considering they only rolled out of the factory with one to begin with…

 

That's the turbo waste gate actuator. Freightliner won't sell you one (sorry bastids!). They want you to buy a whole new turbo. You can find lots of replacement actuators on line and I'm pretty sure I've seen a video on how to replace it. You will have to remove the turbo though.

BTW there are completely crazy price differences. I've seen them as low as $45 and as high as $500.