My truck has always been a little smokey, and with my current injectors I blow a thin layer of soot at an idle, but recently I have noticed this sh*t wont just wipe or wash off. I have to use elbow grease and bug and tar remover. Is it the ULSD, anyone else notice this? Has only happened the last month or so. Could it be because I changed fuel additives to the cummins approved from Genos, and maybe thats it? My poor silver truck looks pretty black in the rear. Ayone else having issues, or any thoughts on the matter....

 

I think I would pull a intercooler tube off make sure you dont have any oil in it may have a turbo seal leaking. I would think the ulsd would be cleaner. Just put 3K with ulsd washed right off. Turbo may not be the problem but I would look for oiling reason(Rings,valve guide seals,so on so on)