Turns out that the problem is in the bottom end on the 6-th cylinder, apparently the engine was not in such a good condition as I though (second hand old engine, guess I should have expected it). Hope to have the engine stripped down by the end of the week and up and running as soon as possible..... will keep you posted

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190E 3.0-24v (M104 980) turbo @ 0.8 bar
1/4 mile: 2.483 / 13.540 / 175.17 km/h (street tires)