The only reason for a diesel to have excessive smoke is either too much fuel or not enough air. I know it sounds stupid, but have you checked your air filter system to see if it's become plugged? I'm assuming you're talking about black smoke and not white/gray (coolant) or blue (crankcase oil.)

If all the other systems are functioning properly, then the injector system is delivering too much fuel and you'll have to have it corrected if the smoke bothers you.