Peugeot 307 exvessive black smoke from exhaust

The first problem that had occured was not starting when cold, had glow plugs done still no luck, had all 4 injectors rested 2 came back as faulty, so got hold of second hand with same part numbers, and they were tested by the garage I had bought them off, it now starts up but there is plenty of black smoke from the exhaust, even if I leave the car unstarted for a few days it will still start up, also the car is mis-firing as I pull off with putting my foot down abit heavy.