my 2007 diesel doblo taxi has 200000 on the clock,it has been burning oil for about 3 months,(have to fill up every 3 weeks)but just this week it has started blow out black smoke,it is not noticeable unless I rev it up then there is a deposit of soot left behind,i have had new oil/air/and a new fuel filter fitted plus the mechanic checked it on a machine (dpf fault) im not sure if the dpf fault would cause the black smoke ?,its due to be tested in 3 weeks and im worried it might fail the emissions test 
