Hi Werner,
Dieselschrauber.de goes worldwide!
Okay, let's talk about your problem:
The injection system in your car is almost identical to that of the VW VP TDI engine (except for having 6 cylinders). I think you might have a problem with the timing of the injection pump.
On the main page of Rainers Turbodiesel's website, you will find a quite good explanation of how to adjust the injection pump without expensive workshop tools.
http://www.dieselschrauber.de/esp.html
I think your German language skills are good enough to understand most of it.
Best regards from cold Germany.
Best regards,
Bertil