Greetings tuned diesel fans. I feel that I should share a tuned diesel experience that I have had. Not a BMW, but the same principles apply. If you are not interested in the back story, just jump to the last paragraph.
My brother and I put a full Banks kit on a Ford F350, it is a very good quality complete kit, tuning, intercooler all new intake and exhaust piping , gauges and fail safes. It also has a dial from 1-6, so you can select how much power you want. Naturally I put it on 6 and left it there.
For its size and capability we don’t use the truck that hard (my company owns the truck, so I am not the only driver, hence the I/we). After about 40,000 miles the truck had some mechanical issues (a HPFP) that required a trip to the dealer for an expensive tear down. ‘While they were in there’ they found that the turbo was ‘coked up’ soot had accumulated on the exhaust side of the turbo and was almost to the point of interfering with the turbo’s operation, it had to be rebuilt.
The truck was rarely smokey even on ‘6’ and the mechanics did not blame the tune and said they had seen this on lightly used heavy duty trucks. It is obvious to me that dumping more fuel on a regular basis isn’t helpful.
Here is what I have done, and what I would recommend. I no longer leave the tune pegged, it is on ‘3’ now rather than ‘6’ and it never smokes even when you floor it on freeway on ramps (the only place it ever smoked a little on ‘6’). The 335d should never smoke with all its high tech-ness so this isn’t a reasonable test for it.
For the 335d I would definitely remove the tune or dial it to its lowest setting before any long road trips. It is important for these modern diesels to get up to temperature and work a little as designed to keep soot from accumulating. I would also dial it down for mountain driving where the engine will be under constant load and have the opportunity to work a little as it was designed to without having excess fuel put into the system.