FrankA8

Hi there, Im new member here. I own an A8 3.0 Tdi 2006 year and i would like to have some help to understand better my engine. Its a V6 engine so i need to know if i need to change every X miles the ignition coils and if the model has fitted DPF. Since recently the car starts to smoke ( dark grey/blackish) and is been done a service just 20 miles ago but still smoke when the car get hot. Is anyone can recommend me what to do and how can fix the issue. Regards FRANK