My c3 hdi has suddenly become a pig to get started. it turns over and starts after about 15 -20 seconds with a cloud of black smoke. It also has started smelling when you switch the engine off and get out you can notice a distinct smell coming from maybe the exhaust. also seems to be using a bit more diesel than normal.

any ides what is wrong and if its expensive or a simple doit yourself job. many thanks in advance