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I've had pretty bad pinging between 1500-2800 for some time and could never quite figure out what was the main cause. Tried all the cheaper options like different fuel, injector cleaners, octane boosters, Italian tune, etc but to no avail. Speaking of injector/fuel system cleaners, the Liqui Moly stuff is amazing. Same driving patterns and after about 3/4 from a full tank of BP98+LM, I went from 14.4km/L down to 13.9km/L. I used to swear by the Techron stuff but I feel the LM is better and I can't seem to find Techron anywhere in Sydney.
Anyway, recently my car developed brake vacuum issues that would cause the car to go into limp mode. This would happen intermittently but most of the time after starting the car cold. Had the vacuum sensor and pump replaced which fixed the original vacuum issue, but to ALL of the workshop staff and my surprise, this reduced the pinging by about 60-70%. Who would've thought brake vacuum issues would also cause pinging? Since fixing the brake vacuum issues, engine runs much smoother in the lower rpm ranges and also feels zippier than before.
At the moment I still have slight pinging from 1800-2000rpm. There was another thread about pre-det and the OP fixed the issue completely with new O2 sensors. This was after OP went through plugs, injectors, maybe coils too but the issue would return. I have a set on order now and will be replacing the pre-O2 sensors when I have the DCT serviced. If you have a scan tool, I would check if either of the 2 pre-O2 sensors are playing up to confirm. These don't need to fail or throw a fault code to cause any pinging it seems.
Thought I'd share my story as I couldn't figure this out for the longest time and the detonation was embarrassing to say the least. Especially so when someone notices your M3 and looks forward to hear the V8, only to hear it rattle away as it goes through the lower rpm ranges.
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