This article draws attention to the problems of maintaining fuel injection pumps of marine diesel engines in the conditions of use of residual fuels whose quality is steadily deteriorating, and also burned under engine’s reduced load and in situations where the international rules require a temporary change over into distillate fuels. The analysis of tribological processes occurring in hydraulic precision pairs of fuel injection pump such as barrel-plunger was presented and the types of occurring wears were discussed based on author’s own operational experience. There was pointed out the need for additional methods of verification / evaluation of technical condition using of technical diagnostic methods.