If it's diesel engine it could be needing new injectors. I drove a B.T. lorry that did that and was stopped by the police for emitting black smoke. Took it to the local B.Telecom workshop and the said it needed new injectors, they put them in an no black smoke. Only a guess mind you. Check with your local library for vehicle workshop manuals some do keep them. Go there if they do and look up any diesel engine faults and see what it says about cause of black smoke before going to the expence of injectors.
Rob
Rob, October 2005
