Diesel Power said:thats caused by one of the reasons i listed
Not always. The carboning on the tips is caused by the combination of ash in the fuel and additives plus lack of enough combustion heat to burn it off. Aside from a mechnaical failure, most carboning issues are by ash build up and not enough EGT's to burn it off.
The lousy fuel we have on top of a lot of these trucks being driven like cars just compounds the issues. Some of the additives being used also contribute more ash than usefullness. Once the carbon buildup is bad enough it then contributes to injector failure. Pressure does not always help when other factors come into play and upset the balance.