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EFI means Electronic Fuel Injection, which injects fuel into the intake manifold to create the air-fuel mixture. It is easier to control compared to carburetors. Most fuel injection systems are electronically controlled, The controller is an electronic control module (ECM) or electronic control unit (ECU). It is also called an onboard computer because it is onboard the car. Various components of the engine and fuel system send electric signals to the ECM. The ECM continuously calculates how much fuel to inject. It then opens the fuel injectors so the proper amount of fuel sprays out to produce the desired air-fuel ratio