Diesel engines have become increasingly popular as a power unit for passenger cars over the last decade, due mainly to their superior fuel economy. The first generation of high speed direct injection engines suffered from a lack of refinement by comparison with contemporary spark ignition engines. Analysis of subjective assessments of typical diesel engine noise identified impulsive sounds and the excitation of low frequency resonances as the major reasons for adverse subjective reaction.In addition torsional resonances in the drive train can be excited by fuelling variations as a result of interactions between hydraulic waves in the fuel injection drillings and pipes (time dependent) and the pump filling and injecting events (speed dependent). Drivetrain resonances can be excited also by rough clutch engagement, road imperfections and sudden increases in fuelling in response to driver demand. These effects have been analysed in some detail and a model-based analysis technique is described which is adequate to develop fuel injection equipment. A parametric analysis identifies the key features in the mechanical components.Combustion noise from diesel engines can be controlled at source by injection rate modulation, as described in a previous SAE paper. Recently refinement targets for diesel engine noise have been expressed as equalling the best spark ignition engine noise Research into subjective assessment of impulsive noise has indicated a method by which improvements to combustion noise may be assessed.