Method and apparatus for operating a fuel injection system

The invention relates to a method for operating a fuel injection system (130), in particular an internal combustion engine (1), in which fuel under pressure in a pressure accumulator (13) is provided and in the pressure accumulator (13) to the prevailing fuel pressure (Prail) by means of a pressure sensor (14) can be determined. According to the invention over a predetermined pressure reduction period (delta_T) away fuel from the pressure accumulator (13) is removed to at least two different time points (t1, t2) during the pressure reduction period (delta_T) pressure values ​​(p1, p2) is determined by the pressure sensor (14) , and determined from the pressure reduction during the period (delta_T) measured pressure values ​​(p1, p2) is (delta_T) closed on an actual fuel pressure at the start of the pressure reduction period.