Blueish or black smoke? Remove the first injector or glow plug and crank the engine over especially if bluish. Could be major failure of the head gasket in the region of the number one cylinder.

It should spit oil out when cranking or the appearance of the glow plug or injector being wet as well is a clue if the gasket has failed. Also a turbo seal might have let go but this should not make the engine run rough.