Electronic Fuel Injection

Electronic fuel injection, almost always abbreviated to EFI, is the system by which a modern engine's fuel supply is governed by electronics rather than by mechanical fuel metering. A network of sensors reports the engine's operating conditions to an electronic control unit, which calculates exactly how much fuel each cylinder needs and commands electrically operated injectors to deliver it. The result is combustion that is far more precise, cleaner, and adaptable than anything the device it replaced could achieve.

That predecessor was the carburettor, a purely mechanical instrument that relied on the suction of incoming air to draw fuel through calibrated jets. Clever though it was, the carburettor could only approximate the correct mixture and struggled to adapt to changing temperature, altitude, and load, making it difficult to reconcile with tightening emissions and economy demands. From the late 1980s onward EFI swept it aside, and by the 1990s carburettors had all but vanished from new cars.

In operation, the control unit reads inputs such as the mass or volume of air entering the engine, throttle position, engine speed and crankshaft angle, coolant temperature, and the exhaust oxygen content reported by the lambda sensor. From these it determines the injector opening time, often called the pulse width, that will deliver the right quantity of fuel, while a separate spark calculation sets ignition timing. Crucially, the oxygen sensor closes the loop: the system continuously trims fuelling to hold the mixture close to the chemically ideal stoichiometric ratio, which keeps the catalytic converter working efficiently and emissions low. It can also enrich for cold starts and full power, or invoke fuel cut-off on the overrun to save fuel.

EFI is an umbrella term covering several physical layouts. Early throttle-body injection used a single injector feeding all cylinders, much like an electronic carburettor. Multi-point or port injection gave each cylinder its own injector spraying onto the intake valve, improving distribution and response. Modern direct injection takes the principle further, placing the injector inside the combustion chamber at very high pressure; whichever layout is used, the governing electronics and sensor strategy are essentially the same.

The advantages over mechanical metering are substantial: easier starting in all weathers, smoother running, better fuel economy, more power, lower emissions, and the ability to self-adjust and even self-diagnose through onboard diagnostics. The trade-off is complexity and a reliance on functioning sensors and wiring, so faults tend to be electronic in nature and are read through diagnostic equipment rather than adjusted with a screwdriver. EFI is now a foundational part of essentially every petrol internal combustion engine, the framework within which all other fuelling refinements operate.