You must connect a diagnostic scan tool to check stored engine codes.

Without codes = guessing could cost you $8000.00 in parts/labor and still not repair the problem.

The G400 CDI engine is known for having vacuum and fuel related issues, this can be the injectors or the high pressure rail system. These engines are very sensitive to fuel quality.


Possible related data:

http://www.justanswer.com/questions/2k979-need-a-european-mercedes-expert-who-is-familiar-with-the