2006 9900Xi with a cm870?

[Chamberpains]

Its a CM870. It has an air operated actuator on the turbo. You need to check for leaks in that system.

Another common problem is the actuator control module failing. Is the boost drop also accompanied with the high stage engine brake being weak intermittently? If so, this can be some of your problem.

Is the EGR functional on the truck or is it demandated? If removed, was the programming done by someone from this site? If not you almost guaranteed have a bad program in the engine. Have it looked at by someone from here. Unilevers or MommaBurt are really good at CM870's.

Your peak boost sounds low also. You need to pressurise the whole engine and check for leaks on the intake and exhaust side. Check the CAC, boots, intake gaskets, exhaust manifold gaskets, joints and turbo gasket. Soak everything down in soapy water.

When was the last time you checked or changed your exhaust pressure sensor or intake pressure sensor? Have you ever? Also check the piping and housing to the exhaust pressure sensor. It gets soot packed and the sensor can't get accurate readings.

What does your air filter look like? Is it in good shape?

Do you have Cummins insite? If not get it. You need it to keep your truck out of the hands of "parts changers". You would be a fool if you didn't aquire it and learn how to properly diagnose simple problems with the engine.