/SUMMARYA description of the main features and current status of the CDI, Controlled Direct Injection System is given. A 2.5l turbocharged CDI engine is compared with its production IDI equivalent by means of vehicle tests. The vehicles, identical saloon cars, were compared on an as-installed basis and, as nearly as possible, on an equal performance basis. Results are presented covering fuel consumption and emissions with European and U.S. fuels over a number of different driving cycles. Drive-by, idle and internal noise levels were recorded. Starting tests were carried out to compare starting, smoke at start and cold idle. An analysis of the cost differences between the CDI and its IDI equivalent is presented.