Ok I've had 2 step colder plugs (NGK BKR5E's) in because I used to spray, but since I sold the kit I never took the colder plugs out and lately I have been noticing my exhaust tip being a little more sooty than usual. So I swapped my Platinum plugs back in and in doing so I saw that the 3 Left bank plugs (which I'm assuming is the front bank) were completely coated black soot and the white ceramic had just started to brown.., but then my right bank 3(rear bank 3), were almost perfectly clean!.. I think I got build-up issues, but i'm not sure what I do to fix this.. and why is it only in the front bank?

any advice helps thanks..

 

2 steps colder are BKR7E..

BKR5E are stock heat range plugs

 

thanks.