Black smoke and no performance on MB 814, what is the error?

Hello, I hope that I can find a resourceful RATGEBER here, the workshops are apparently overwhelmed with it, grrr. I have an MB 814 Bj 92, it has always run flawlessly. After a stop and another start he suddenly had no more power, he drives only 50 km/h and smokes extremely black. I first thought it was the fuel filter, new—– then new air filter, also no improvement. In the workshop then diesel pumps test and also the injection nozzles were tested and are ok—-tja only running he does not to this day. Who knows then?????—–I have read something about a flame starter, can it be that he gets too much diesel over it in case of defect and therefore so smokes and does not pull? I assume that he gets too much diesel in relation to the amount of air, must also be as the engine gets quite hot. Would really be great if I could get some information here, am already despairing. Thank you very much in advance.