Hi, following the storm, I had to get a scaffolder out to discuss roof repair.
He's got a tdv8 from 07. Lovely.
He has black smoke on acceleration viewable in his mirrors and it's low on power.

Anyone willing to point to probable causes?

Sounds like a typical syndrome for splitted intercooler hose.. Did he check already? Current:
- 2006 RR L322 - 3.6 TDV8
- 2022 MB AMG GT BS
- 2020 Audi Q2

Past:
- Ferrari California 30
- 2018 Abarth 595 Competizione
- 2009 Porsche Cayenne Diesel
- 2010 MB E500 Coupé
- 2005 Porsche 996 Turbo
- 2002 Porsche Boxster 986 S
- 2001 Audi S8

Or cracked inlet manifold.

Split Intercooler hoses easiest thing to check, I had exact same symptoms;

Click image to enlarge

Thank you guys. I shall let him know.