Black smoke

I got myself a titanium plus in diesel. Have driven 15000 kms so far. The car is an absolute delight to drive. Superb acceleration and handling, feels very planted even at high speeds. However, when I try to accelerate from 2nd to 3rd gear, on releasing the clutch while shifting gears, there is black smoke coming out of the exhaust. Similarly when I accelerate on the 3rd gear, black smoke comes out of the exhaust. Having such a great car, I dont really feel good when this happens cos I have seen 8-10 year old diesel cars running without such problem. My Ford service centre have not been able to rectify the problem so far and that is the most disappointing.