black and white mix smoke comes out from exhaust and engine sound is diffrent

Question

this is a isuzu npr85 A/T truck converted in to a manual, when do the diagnostic scan for the first time report showed up an EGR fault.then i did EGR off from ECU (4JJ1-1).then EGR and other faults got clear but P0079 still there and also heavy black smoke still comes. this is a new engine with low mileage.Im pretty sure that engine is not worn and injectors are totally fine.where will be the problem? which components should i check?