Why do fuel injectors stay open?

Fuel injectors do not stay open. They are designed to open and close very quickly, in order to precisely control the amount of fuel that is injected into the engine. When an injector is open, it allows fuel to flow from the fuel rail into the engine's combustion chamber. When the injector is closed, it stops the flow of fuel. The duration of time that an injector is open is called the injection pulse width. The injection pulse width is controlled by the engine's electronic control unit (ECU), which calculates how much fuel is needed based on the engine's operating conditions.