Electronic Fuel Injection

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Electronic fuel injection or EFI was introduced to the automotive world in the 1950s. The Chrysler Corp. offered the electro-injector as an option on its hemi V-8. Shortly after its debut reliability problems forced Chrysler to recall the few systems that sold.

Ironically, recalled vehicles were retrofitted with two four-barrel carburetors that had secondaries the size of dinner plates (exaggeration). Chevrolet as an option on their flagship Corvette models made one of the most famous early EFI systems.

image of fuel injected corvette

Although worth a ton of money now, they abandoned the system not due to reliability issues, but instead lack of sales stemming from a low level  of consumer confidence in this brand-new system. Changing the fuel delivery system from something that worked great was a tough pill to swallow for car makers.

Three decades later the tide would turn when manufacturers abandoned the carburetor in favor of the electronic fuel injection system. The return of the fuel injection system was necessary for the vehicle manufacturers to meet the ever-increasing corporate average fuel economy (C.A.F.E.) standards mandated by the government.

Fuel Injection Systems

There are two basic types of EFI systems, including throttle body injection or TBI and multiport fuel injection or MFI. In a TBI system, one or two shower head type injectors depending on the engine size are mounted above the throttle plates of a single or dual barrel throttle body.

Similar to a carburetor, atomized fuel is delivered above the throttle plates and distributed throughout the intake manifold. Although throttle body injection is more efficient than the carburetor it shares the inherent problem of uneven fuel distribution common to all the wet type manifold designs. With multi-port fuel is delivered directly to each cylinder via individual injectors.

The intake manifold is then used exclusively for air induction called a dry intake system. The injectors are mounted on the manifold so the injector nozzles are aimed at the backside of the intake valves. This arrangement provides a significant improvement in overall engine performance over the previous throttle body injection designs.

How Electronic Fuel Injectors Fire

image of fuel injectors

Depending on the application the injectors in an electronic fuel injection system may be fired simultaneously, in groups or even one at a time. The simplest configuration is to fire all of the injectors at the same time.

With this method each injector is fired once every crankshaft revolution, which results in two shots of fuel per combustion cycle. This method is used generally on single or dual throttle body injection systems. On multiport fuel injection this strategy is known as bank firing. This method separates the odd and even number cylinders into two separate groups.

The injectors in each group are fired simultaneously while the groups are fired separately. This system has since been replaced by the most popular method of firing multiport fuel injectors. SFI stands for sequential fuel injection With this method, the injectors are fired one at a time when the time is right.

Sfi injectors are fired in the same firing order as the spark plugs. Unlike simultaneous and grouped injection, sequential fuel injection systems require a cylinder identification signal to initiate injector sequence or pulse to open the injector.

The most common way to produce this signal is with a camshaft position sensor or a synchronization slot cut into the crankshaft sensor magnetic ring. Most of the 1996 and up OBD two systems use this sequential fuel injection system. This is currently the most efficient way to supply your engine with fuel.

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