The invention relates to an electromagnetically controlled measuring apparatus for the volumetric measurement of the quantity of fuel injected by a fuel injection pump that has a displacement transducer which is surrounded by cooling chambers. The apparatus also includes a differential coil pair and a magnetically conductive core, which can be guided axially therein. The coil and the conductive core constitute part of a lifting rod connected to a measuring piston, with a coil carrier and a housing surrounding the coil carrier. The magnetically conductive core consisting of a ferritic material and being firmly surrounded by a sleeve, which forms the lifting rod, is not magnetizable and is provided with a slot extending continuously in the longitudinal direction of the sleeve.