A fuel injector having a fuel inlet, a fuel outlet, and a fuel passageway extending along an axis between the fuel inlet and the fuel outlet. The fuel injector includes a body having an inlet portion, an outlet portion, and a neck portion disposed between the inlet portion and the outlet portion. An adjusting tube is disposed within the neck portion of the body. A spring is disposed within the neck portion of the body, the spring having an upstream end proximate to the adjusting tube and a downstream end opposite the upstream end. A filter assembly is disposed within the tube assembly to provide a reaction member for the spring. An armature having a lower portion is disposed within the neck portion of the body and displaceable along the axis relative to the body. The downstream end of the spring is disposed proximate to the armature, the spring applying a biasing force to the armature. A valve seal is substantially rigidly connected to the lower portion of the armature. The fuel injector includes a modular valve group subassembly that is connected to a modular coil group subassembly.