^ Thanks Xulfiqar bhai for your ever-helpful info.
Sir I live in Abbottabad. There is a hill climb of around 15 Km when approaching abbottabad. What I meant by black smoke is this: if you feel. while going up a slope. that you are loosing speed the natural instinct is to press the accelerator. But 9/10 times this results in black smoke coming out of your exhaust. This implies wasting of fuel, just like you said "excess fuel" but not enough air pumped in by the turbo as yet. There are two proper ways of doing things
1. Just make a compromise on speed and let off your accelerator a bit so that the fuel is not wasted. Or press ur accelerator gently and slowly, small step by step so that the turbo can keep up with the increasing amount of fuel coming in.
2. Shift down a gear and then press the accelerator gently step by step. You will notice that there is no more black smoke - provided the engine / pump are fine.
I hope Xulfiqr Bhai will shed light on BLUE smoke in diesel engines and tell us that it implies burning of Engine Oil and some other problems and NOT unburnt diesel as someone mentioned earlier.
By the way Xulfiqar what is this ATF stuff? It would be kind of you if you explained.
Regards to all