A fuel injector (1) is provided which comprises a valve member (11), a valve member guide (12) and a spring chamber (40). Discharge of fuel out of a fuel injector outlet (21) is controlled by movement of the valve member (11) within a bore (23) of the valve member guide (12). The spring chamber (40) contains a biasing member (50), for example a compression spring, which biases the valve member (11) into contact with a valve seat (20) when in a closed configuration.

A fuel supply passage (80) is provided, which by-passes the spring chamber (40), to direct a flow of the fuel to an outlet chamber (22) of the fuel injector (1) and a cleaning fluid supply passage (90) is provided to supply a pressurised cleaning fluid to a second end (25) of the bore (23) to restrict leakage of the fuel from the outlet chamber (22) towards the second end (25) of the bore (23) along a clearance (29) extending between the valve member (11) and the valve member guide (12).

A fuel injector is provided. The fuel injector includes a sleeve having a first end proximate an outlet; a piston slidingly received in the sleeve, the piston having a first end proximate the outlet; a pumping chamber at least partially defined by the sleeve between the first end of the piston and the outlet; and a normally-open inlet valve through which fuel passes to enter the pumping chamber.