A method includes: filling a chamber having a recirculating valve, a piston, a cap valve, an injector valve and an injection orifice with a liquid by closing the injector valve and circulating the liquid from a source through the recirculating valve and the cap valve; then isolating the chamber from the source by closing the recirculating valve and the cap valve then allowing pressure within the chamber to follow a cylinder pressure by mechanically coupling the cylinder pressure into the chamber; and energizing an injector coil with electric current that pulls a solenoid assembly in an upward direction opening the injector valve, further motion of the solenoid assembly drawing the piston upward, wherein liquid in the chamber is compressed by the piston to a higher pressure than the cylinder pressure, which has the effect of injecting an electronically controlled stream of liquid out of the chamber through the injection orifice.