Yesterday while applying wool wax to the underneath of my 21 I noticed soot/carbon on the tip and inside the tailpipe. I just turned 5k on this thing, 2.5 not the turbo version. I know these are now DI versus my 18 rogue which is not and has a spotless tailpipe at 45k. I’ve never owned a DI engine so this may certainly be normal, but in the old days meant an incorrect fuel air mixture, or worse stuck rings or valve issues. The oil level appears normal as it only has 100 miles on my 5k oil change. Although the dipstick on this thing is next to worthless as far as getting an accurate measure. Anyone else seeing carbon buildup on the new engine design or do I have a future issue in the making?

Just about everything GDI builds up superficial carbon throughout the system, but we haven't seen anything excessive on the new Alties. With GDI's in general, when buildup problems do occur, it's usually at the valves, specifically on the backs of the intake valves. Routine de-carboning is a good idea every 30K or so.

What do you suggest for decorboning? The owners manual is the typical Nissan jargon. “Oil that meets SN GF5 and Nissan doesn’t recommend fuel treatments”.
My wife’s 18 just had a slight idle fluctuation and I used a bottle of techron and it cleaned right up. Unless we are on the road we always fill up at the same marathon (top tier fuel) so I use quality oil and gas and change it regularly. The last car I had that had a dirty tailpipe was an 08 impala that burnt a half qt every few k

My technique (and most others at our shop) is a teaspoon of ATF down any vacuum orifice with the engine warm and held at 3500~4000 RPM. The mineral oil creates a temperature differential in any caked carbon that fractures it and breaks its adhesion, letting it burn up in the cat.