Abstract: A fuel injector for a fuel injection system includes a nozzle body defining a nozzle body chamber, a needle movably received within the nozzle body chamber for movement between a seated position and a raised position, and a needle sleeve at least partially surrounding the needle and at least partially defining a control volume. The needle moves from the seated position to the raised position in response to a pressure differential between the control volume and the nozzle body chamber. When the needle is in the seated position clearance exists between the needle sleeve and the needle thereby permitting fuel flow between the control volume and the nozzle body chamber, and when the needle is in the raised position, the needle sleeve deforms to reduce the clearance and restrict fuel flow between the control volume and the nozzle body chamber.