A fluid injection system for use with a syringe is disclosed. The fluid injection system includes a housing, a drive member at least partially disposed within the housing, at least one radially retractable pin disposed within the drive member, and a sensor positioned to sense rearward movement of a sensing pin in the drive member. The at least one pin is adapted to form a radially retractable abutting connection with a plunger of the syringe in response to axial movement of the drive member. Further, at least a portion of the pin is radially extendable and retractable through at least one radial passage in the drive member, and is retracted within the radial passage during forward movement of the drive member, and extends radially outward through the radial passage during rearward movement of the drive member.