Ever increasingly stringent emissions regulations throughout the world mean that manufacturers have to pay more attention to the emissions performance of both spark ignition and compression ignition engines. Electronic engine management systems allow close control engine operating parameters, providing a means for tuning engines for low emissions with minimal costs in terms of performance.The aim of this paper was to quantify the effect of two tune parameters, start of injection timing and EGR rate, on the exhaust emissions of a modern, electronically controlled high speed direct injection diesel engine. The paper will present emissions data taken from the engine running at two speeds and load combinations representative of typical engine operating conditions during the European emissions cycle. At each of these points the tune strategy was varied and the results observed. The impact of varying start of injection timing and EGR rate on emissions and engine performance was investigated and both were found to have a significant effect on engine efficiency and emission performance.