Apparatus and methods for injecting gaseous fuel into a compression ignition engine are disclosed. A gaseous fuel injector includes a pintle valve and an intensifier. The pintle valve includes a pintle body defining a pintle bore therethrough, a first sealing surface disposed on a distal end of the pintle body, and a pintle disposed within the pintle bore. The pintle includes a shaft, a radially flared portion, and a second sealing surface disposed on a proximal face of the radially flared portion, such that the first sealing surface faces the second sealing surface. The intensifier includes an intensifier body defining a fuel pump chamber therein, the fuel pump chamber being fluidly coupled to a gaseous fuel supply and the pintle bore, a plunger having a distal end disposed in the fuel pump chamber, and an intensifier piston disposed on a proximal end of the plunger.