The contribution to the noise of automotive diesel engines from the DPA rotary fuel injection pump has been assessed by comparing its overall noise with that of a number of engines, to which the pump is, or may be fitted. From this data, a ‘worst case’ has been selected for a more detailed assessment. The noise generating mechanisms of the pump are examined. Two improvements are described which are suitable for mass production with existing facilities, and which reduce the overall noise by 3 to 5 dB (A). An outline of a modular mathematical model is presented which will guide future efforts towards further practical cost-effective noise control.