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Electronic Fuel Injection 101

Fuel Injectors

Electronic fuel injection has been the basic standard for most automotive engines since the mid-1980s and is a source of confusion for many do-it-yourself mechanics due to the perceived complexity of the system. Once you have a core understanding of how fuel injection works, however, it becomes much easier to diagnose and repair problems it may have.

The basics are pretty straight forward: fuel and air are mixed and injected into the cylinder for combustion. There are three basic types of fuel injection: throttle body, multiport, and GDI.

Throttle Body Injection

This is now the rarest of fuel injection types, as it was the first fuel injection to take over from caburetors in the mid-1980s. Injectors are mounted in the throttle body and spray fuel into the intake manifold to mix with air. Fuel pressure is created by the pump, usually located in or near the fuel tank, and a regulator mounted to the throttle body itself. Fuel is sprayed in short bursts, controlled by the engine computer (ECM).

Compared to other methods, throttle body injection is relatively inefficient and often creates "lean-rich" spectrums that differ between cylinders, just as they do with a carburetor.

MultiPort Fuel Injection

The most common type in today's modern automobiles, MultiPort has separate injectors for each cylinder and fuel is sprayed directly into the intake port of the cylinder to be mixed with air in the cylinder's combustion chamber. This is far more efficient than injecting fuel into the air intake, as with carburetors and throttle body injectors.

MultiPort fuel injection is entirely computer controlled, though early systems used mechanical controls (think 1957 Corvette). Until the mid-1990s, MultiPort injection systems often fired all injectors on a cylinder simultaneously, but today, they are often precisely controlled with each cylinder's injector firing at different rates or pulses in order to maximize mixture as well as firing need for that specific sequence. This came with SFI (sequential fuel injection), which replaced EFI (electronic fuel injection).

Gasoline Direct Fuel Injection

Beginning with the turn of the 21st century, GDI began to become more common in automotive applications, especially with European vehicles from the Volkswagen Group and others. The main difference between GDI and MultiPort injection is that GDI injects directly into the combustion chamber rather than the intake port. This requires specific fuel injector heads to withstand the combustion chamber's pressures and heat, but results in far higher fuel economy and power output thanks to the more precise control of fuel:air mixing it allows. Vehicles utilizing GDI can see 15 percent or more improvement in their fuel economy alone.

In another installment, we'll talk about fuel injector timing.