Future emission standards for heavy duty diesel engines will require the application of improved fuel injection systems with high pressure capability and electronic control of timing and fuelling. A recent Ricardo research project has concentrated on the application of the latest in-line pump from Robert Bosch, designated RP39, to a prototype turbocharged and aftercooled heavy duty diesel engine based on the Volvo TD122. The maximum pressure capability of the prototype RP39 used during the experiment was 1400-1500 bar at the injector nozzle. The pump also featured electronic control of the injection timing and rate by the sleeve control principle. The RP39 was matched to a revised low swirl combustion system. Results from steady state and transient tests are presented highlighting NOx/fuel economy/particulate trade-offs and their response to injection pressure, rate and timing, leading to a demonstration of how 1991 engineering targets for NOx and particulate were readily achieved and the 1994 legislative standard approached with limited development. The potential for further improvement is discussed.