The term Mechanical when applied to fuel injection is used to indicate that metering functions of the fuel injection -how the correct amount of fuel for any given situation is determined and delivered- is not achieved electronically but rather through mechanical means alone. All the components in both mechanical or Electronic Fuel Injection (EFI) systems that deliver the fuel in to the engine -the pumps, plumbing, valves, injectors- are mechanical in operation. The difference being that in EFI systems the injectors are switched on and off electronically by the EFI control electronics. This ability to control the injectors electronically allows far more variation in when and how the fuel is injected.