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Electronic Fuel Injection - EFI For The Masses

Is Electronic Fuel Injection For Everyone?

If you paid attention to nothing more than what type of vehicles the OEMs are building today, then you'd think there wasn't any other way to fuel your car besides electronic fuel injection (EFI). The fact that a carbureted car has not left Detroit since 1985 would lend one to think that carburetors are surely a thing of the past. But are they? And why has EFI become the staple of auto manufacturers worldwide? Is it that much better than a carburetor? It surely can't cost less, because you can tell just by looking at the stuff that EFI is expensive. And aren't the OEMs always looking for the cheapest way to build the best cars they can?

In reality, the automakers have one major factor to thank for EFI: smog. That's because without the strict emissions rules placed on the manufacturers back in the '70s and '80s there would never have been a reason to further develop EFI. We use the term "further develop" here because EFI was around automobiles long before 1985. Several companies tried to mass-produce EFI systems for the mainstream many years ago, but at the time they were too expensive and impractical to last.

Then, Big Brother stepped in and told the OEMs they had to clean up their act. Since most vehicle emissions are produced when the car IS NOT at wide open throttle-the big pollution comes from cars idling and cruising around town-the OEMs had to figure out a way to clean up emissions in those highly critical areas. EFI was the answer.

What Is EFI?
It's important not to confuse today's electronic fuel injection with the mechanical fuel injection systems used in the past and still in use on some of the highest-output race engines in the world. The fuel injection that powers our cars today is called EFI because the injector pulses are controlled electronically, not mechanically. That means there's a small, yet very powerful, computer in your car that controls how much fuel the engine gets. That same computer also controls your ignition advance so there are no more little springs and weights in the distributor (that is, if your car even has a distributor).

Ironically, the computer still needs input from both you and the engine to correctly meter the fuel and set the advance curve. Things like throttle position, temperature of the air inside and outside the engine, manifold pressure or vacuum, oxygen content in the exhaust, coolant temp, and even the amount of air flowing into the engine all play a critical role in how the ECU meters fuel. One thing that the computer does not control, except in a few limited OEM applications that have just come out, is fuel pressure. That's still controlled by a good old-fashioned regulator, which may be pressure-referenced off of the intake manifold. Typically, a pressure-referenced regulator will increase fuel pressure at zero intake manifold vacuum or, in the case of a supercharged engine, when there's boost in the manifold.

The natural effect of more fuel pressure in an EFI system is more fuel sprayed for the same injector pulse duration (we'll explain more about that in a minute) and a richer mixture. It's kind of like the power valve enrichment circuit in a Holley carburetor. At WOT the engine needs much more fuel than it does at cruise, so the power valve, or in EFI's case the extra fuel pressure, adds that much-needed extra fuel. Ironically, it's one part of an EFI system that is still mechanically controlled.

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