Thanks guys for all the input. Realy helped me out. I am planning to take off the cat anyway becouse the flex joint needs replaceing (thank god the inspector didnt notice it) and will inspect everithing then.
Ok today l drove a bit to heat the engine and dispach the oil/diesel mix trugh the engine and drained it. Black like hell! Then filled the crankcase with 3l of pure diesel, started the engine to idle for 10s, still black. This procedure was repeated 3 times untill the diesel drained rather clean. Put new oil in.
The resault? Engine runs better, and the crankcase vent expells much less gas. Allso, today a coworker mentioned that he smelled oil when l drove by. Today l asked my wife to crank the engine with my face at the tailpipe (looked ratrer suicidal ). No smell of oil.
Compression went up on all 4 cyl, althugh 2 are still worst thain the other 2. Well not ideal but better.
Question: what do you guys think, what is No1 cause for such happenings?
My thods are tar, soot or woodgas itself (forming carbon at high pressure)
Tar l think is most possible, but it beats me that l have never seen any tar anywhere else in the assembly.