Just seen today a Subic Pajero when accelerating lot of black smoke on the tail pipe it produce that a problem on smoke belching . Is this really a problem on diesel engine which a lot of owner complain. Yes, many diesel owners complain of black smoke. But this problem is due to poor maintenance.
Properly maintained diesels don't emit black smoke.

Is this also the cause of consuming a lot of diesel gas. Partly yes. Black smoke is a sign of rich fuel mixture, either due to overfuelling, or due to insufficient air to the engine.