I can't say anything good or bad about Liqui Moly or other brands as I haven't tried using any. If you want to try it out, just make sure that it's a diesel injector cleaner, and not a petrol injector cleaner. And I suggest these:
  1. Replace and invest on an original Mits air filter
  2. Check tire pressures and remove any unnecessary weights from your car
  3. Fill up with clean diesel only, then log your consumption, exhaust quality, and power
  4. Fill up with clean diesel, add injector cleaner in the proper ratio, then log data as you previously did
  5. Then post your experience in this thread. This will be a great help to fellow Tsikoters.
Btw, the 4M40's fuel injection system is sturdy and quite tolerant to our fuel quality. It is the newer diesel injection systems which are quite sensitive to fuel quality.