So I'm gonna have to add some more input on this thread after doing extensive research on another factor than can cause cbu. So we all know a major constituent of the carbon build up in the intake is from the soot recirculated into the intake by the egr.
So what causes soot on a diesel. There are some good papers written by chevron and others researching the phenomenon.
http://www.chevron.com/documents/pdf...TechReview.pdf
Anyway suffice it to say it is made up primarily of unburnt fuel and oil in the cylinders. Why do we have unburied fuel?
Low cetane fuel is more likely to form soot, the lower the cetane the more likely the fuel isn't going to completely combust.
Clogged injectors that don't properly atomize the fuel which leads to fuel droplets in the cylinder not mixing with air and being converted into soot when exposed to combustion temps
Low engine temps
Oil in the engine that easily evaporates into the combustion chamber and possibly weak oil rings. Aka engines that drink oil will generate more soot.
So basically, keeping your injectors clean and using high centane fuel are the major factors we can contro, and yes fuel quality can make a difference in soot formation, and volume that gets sent through the egr.
Basically,
Low cetane fuel, egr, pcv sending lots of oil, turbos leaking, valve stem seals leaking, and materials that allow soot/oil/carbon accumulation to adhere to the surfaces are the problem areas. Eliminating egr will help to reduce the amount of soot in the intake. But it's not the only source of the problem.