Method for the operation of a high pressure pump in a system for fuel injection in a combustion engine, wherein said high pressure pump comprises at least two pump elements, which are connected in parallel between a low pressure part of the system and an accumulator tank for fuel injection to the combustion engine, and each has a cylinder with a pump chamber with a moveable piston therein for pumping, and an inlet valve arranged in this cylinder's connecting opening to the low pressure part, which valve may be controlled in order to control the flow of fuel into the pump chamber characterised in that it comprises the steps a) to determine whether a predetermined partial load condition prevails in the combustion engine, at which one single of said pump elements is capable of alone delivering a fuel pressure requested in the accumulator tank according to a first reference value (P 1), and to achieve a reproducible increase of the fuel pressure to a second reference value (P 2), and if this operating condition prevails, to continue the method with b) controlling the high pressure pump's pump elements, so that one single of the pump elements alone delivers a fuel pressure in the accumulator tank according to said reference value (P 1), c) changing of the reference value for the fuel pressure in the accumulator tank to the second reference value (P 2), while the control of the pump elements is maintained so that said single pump element alone delivers the requested fuel pressure in the accumulator tank, d) during the build-up of the fuel pressure in the accumulator tank from the first reference value to the second reference value, determine the fuel pressure in the accumulator tank as a function of time, e) comparing of the development of the fuel pressure in the accumulator tank, while the fuel pressure builds up therein, with stored values of such developments, in order to determine information about the pump element's performance ability, and wherein steps b)-d) are carried out in all the pump elements of the high pressure pump, at different times when a said predetermined partial load condition prevails, and for each pump element in step e) the development of the fuel pressure in the accumulator tank is compared, as a function of the time at the change of said reference value from the first to the second, with this development in this or the other pump elements, and based on this comparison the pump elements are ranked according to efficiency. a) to determine whether a predetermined partial load condition prevails in the combustion engine, at which one single of said pump elements is capable of alone delivering a fuel pressure requested in the accumulator tank according to a first reference value (P 1), and to achieve a reproducible increase of the fuel pressure to a second reference value (P 2), and if this operating condition prevails, to continue the method with b) controlling the high pressure pump's pump elements, so that one single of the pump elements alone delivers a fuel pressure in the accumulator tank according to said reference value (P 1), c) changing of the reference value for the fuel pressure in the accumulator tank to the second reference value (P 2), while the control of the pump elements is maintained so that said single pump element alone delivers the requested fuel pressure in the accumulator tank, d) during the build-up of the fuel pressure in the accumulator tank from the first reference value to the second reference value, determine the fuel pressure in the accumulator tank as a function of time, e) comparing of the development of the fuel pressure in the accumulator tank, while the fuel pressure builds up therein, with stored values of such developments, in order to determine information about the pump element's performance ability, and wherein