A method and to a device for operating a pressure reservoir, where during a compression phase in a pump chamber, a pump periodically increases the pressure of a fluid located therein, and by means of a discharge valve controlled by differential pressure fluid under high pressure is allowed to be introduced from the pump chamber into the pressure reservoir. During a decompression phase following a compression phase, fluid from a fluid reservoir is introduced into the pump chamber by means of a controllable intake valve. In order to be able also to operate the pressure reservoir without a high pressure measurement directly in the pressure reservoir, the fluid pressure in the pressure reservoir is ascertained by means of a pressure determination in the pump chamber. The pressure determination takes place indirectly, monitoring of the intake valve in the decompression phase.

When a plunger of a high pressure pump is rising, a high pressure pump controller closes a regulator valve by energizing a solenoid of an electromagnetic actuator of the high pressure pump to discharge fuel into a delivery pipe. Further, this fuel discharge energization is stopped before the plunger reaches top dead center at a pump TDC timing. Further, a fuel pressure of the delivery pipe is detected at the pump TDC timing, and based on that detected value, a time Td from the pump TDC timing until a valve opening timing of the regulator valve is estimated. Once the estimated time Td elapses from the pump TDC timing, the solenoid is reenergized to removed a movement speed of a movable portion in a direction that pushes the regulator valve in an opening direction.

Systems and methods are provided for operating a direct injection fuel pump. One example system comprises an accumulator positioned within a bore of the direct injection fuel pump in a coaxial manner wherein the accumulator is positioned downstream from a solenoid activated check valve. The accumulator may regulate pressure in a compression chamber of the direct injection fuel pump and a high pressure fuel rail when the direct injection fuel pump is operating in a default pressure mode.