Black smoke is unburned fuel (too much being injected against the amount of air) . A quality custom map should smoke very little (or not at all) (R-Tech Nick will do you a proper map )
Iv always seen diesel smoke as normal, which is why we have these DPF's.
R-Tech did do my MK4 and i was very pleased with it. Im up that way at the end of the month again so might fly in for a chat.
ANther question is MPG, with my previous car it was improved a lot, will i also see this on the new car?
I average around 45mpg to the tank at the mo....
cheers