A lubricant injector includes a body having an inlet fluidly coupleable to a lubricant source, an outlet, and an elongated bore extending along an axis and having an outer end proximal to the body second end, a closed inner end spaced axially from the body first end, a first port, and a second port disposed generally between the bore closed end and the first port. A delivery chamber separate from the bore has an inlet port and an outlet port fluidly coupled with the body outlet. A piston disposed within the bore divides the bore into an operating chamber coupled with the first port and a measuring chamber coupled with the second port. The operating chamber is fluidly coupled with the inlet and the measuring chamber is located between the bore closed end and the operating chamber and is fluidly coupleable with the inlet and alternatively with the delivery chamber.