Hi Werner,
Dieselschrauber.de goes worldwide!
Well lets talk about your problem:
The injection system of yor car is nearly the same as in the VW VP TDI engine (exept of having 6 cylinders). I think you have a problem with the injection pump timing.
On the mainpage of Rainers Turbodiesel page yo 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 yout German language is good enough to understand most of it.
Viele Grüße aus dem kalten Deutschland.
Kind regards Bertil