The main problem is generated by the poor quality fuel we put in our cars, if you look at European diesels which have been running for 200K+ don't have the same deposits as North Americans engines do as European Brent fuels are higher in octanes (European premium 98 octane, NA premium 91 to 93 octane) plus they have additives in there to help clean this ever advanced motors. Going back to our diesels, euro diesel has a higher level of cetane in it to prevent carbon deposit by cleaning valves and combustion chambers, luckily in Canada shell has introduced the V-Power diesel which has the same values as the European diesels (higher level of cetane, de icer, and other additives). This is the only diesel I use for my 335d and 320Cdi, I can tell the difference from a period where I was using cheap discounted diesel for my 320Cdi (daily driver) and after a few months the check engine came on, it was the computer putting the engine on safe mode (reduced power) for improper fuel injection, cleared the problem went back to V-Power diesel with no problems ever since. I'm not sure why shell does not offer this quality diesel in the US but the regular highway diesel sold there is really bad for our 335d and Im not surprised to see all these carbon problems you guys are talkin about. The other way to solve the problem is to use Liqui Moly additives every once in a while to correct the cetane level in your tank. So the reality is that the 335d engine has no faulty design (heads, injectors or EGR), the main issue has to do with the poor quality fuel and the DPF does worsen the situation so removal won't be a bad idea, plus methanol injection would be ideal if someone has come up with kits for our cars
