Deposits formed on the plungers, barrels and delivery valves of some in-line injection pumps in diesel engines. The deposits formed during 5,000 - 20,000 km of driving and caused sticking of plungers. Normally the plungers, barrels and delivery valves keep clean. Deposits formed if kerosene based arctic diesel fuel containing lubricity additive was used.Small amounts of engine oil mix with diesel fuel in the pump. A chemical reaction between the fuel lubricity additive and the engine oil, which lubricates the camshaft of the pump, caused the deposits. The problem was avoided by changing the type and dosage of the fuel lubricity additive.