The injector itself is a normally closed valve (the normally closed valve means that the valve is always closed when no control signal is input; the normally open valve means that the valve is always open when there is no control signal input). A valve needle moves up and down to control the opening and closing of the valve. When the ECU issues a fuel injection command, its voltage signal will cause current to flow through the coil in the fuel injector, generating a magnetic field to suck up the valve needle, allowing the valve to open so that fuel can be sprayed out from the fuel injection hole. The biggest advantage of injection fuel supply is that the control of fuel supply is very precise, allowing the engine to have a correct air-fuel ratio under any condition. Not only does it keep the engine running smoothly, but its exhaust gas can also comply with environmental regulations.