I have a DT 530, we did complete overhaul in nov, new inj. as well, now truck came in kncking and blowing black smoke, we pulled exhaust man started it, found #4 smoking bad, replaced #4 inj. now still has a little miss and engine sound like it wants to come appart at idle, as soon as you raise it off idle or load up the eng noise goes away, I suspect faulty inj. I have a scanner comming in in the morning so i can do a cut out test, any sugestions?