fluid out of the upper fluid chamber 246 through the orifice 250 the action of the liquid fuel flowing out of the upper fluid chamber 246 acts as both a temperature compensator and damper for the piezoelectric injector in a second embodiment the fuel injector is actuated using a pressure differential the fuel pressure in the lower chamber 246 is different than the fuel pressure provided to the temperature compensator 240 in this embodiment the fuel pressure in the lower fluid chamber 216 is higher than the fuel pressure in the upper fluid chamber 246 which biases the injector pin 205 to an open position in an alternative configuration the fuel pressure provided to the lower fluid chamber 216 is lower than the fuel pressure provided to the upper fluid chamber 246 so that the injector pin 205 is biased to a closed position referring to fig9 12 in a third embodiment the fuel injector is actuated using damping fluid at the temperature compensator 240 in this embodiment pressurized damping fluid with a higher viscosity than fuel is used in the second fluid chamber 604 and third fluid chamber 606 fuel is pumped into the fourth fluid chamber 612 which causes the injector pin 205 to be biased to a closed position fuel or other pressurized gas is pumped into the lower fluid chamber 216 at a pressure substantially equal to the fuel or gas pumped into the fourth fluid chamber 612 and the pressure of the damping fluid biases the injector pin into an open position the opposing forces of the fuel in the lower fluid chamber 216 and the fourth fluid chamber 612 combined with the damping fluid pressure hold the injector pin 205 in a pressure neutral state in a fourth embodiment the.