Electronic Fuel Injection

Electronic Fuel Injection

No more carburetors?and here's why

Imagine you're looking over the shoulder of an early pioneer of the computer industry. He's sweating over thousands of cathode-ray tubes all spaghetti-wired together, trying to cobble up a contraption that the simplest laptop PCs now outperform on giga-fold scale. Then you whisper in his ear, "You know, some day you'll see this sort of machine controlling the engine of every new car." The bespectacled engineer would probably have you hauled off by a security guard and thrown in the loony bin-yet that is exactly what has come to pass.

The last carbureted cars rolled off the assembly line several years ago. Today, electronic fuel injection (EFI) is the standard of the auto manufacturing industry. Not only that, but EFI is taking over the aftermarket for hot rodders, traditionally the bastion of old-tech hardware. When Tuned Port Injection first appeared on Camaros and Corvettes about 15 years ago, hot rodders could hardly wait to unbolt the tubular manifolds and yank out the nest of wires and sensors in order to install a more familiar carburetor and intake manifold. "No way I'm giving up my 650 Holley double-pumper!" they might have snorted.


Now old-guard hot rodders admit that EFI has a number of performance advantages, something already realized by the younger performance crowd that has grown up without ever having to fiddle with carb screws to adjust the air/fuel mixture and idle speed. The reason for the change is simple: EFI simply works better. A computer-controlled engine is easier to start and is more drivable, with less hesitation and stalling. Added bonuses are increased fuel efficiency and reduced emissions, too. Not only that, an EFI engine can respond more quickly and precisely to the changing boost levels of turbos or superchargers as well. Offroad enthusiasts love EFI, too, for its consistent fuel delivery, even on steep inclines and bumpy terrain.

For those not familiar with the technology, the system is not as baffling as that early computer engineer might have thought. Yes, there's a mysterious black box that's the brains of the outfit, but its job is fairly straightforward. This ECU (electronic control unit) does the same thing a carburetor is supposed to, only better, way better. It maintains an extremely precise air/fuel mixture, ideally at a 14.7:1 ratio, but that varies with engine conditions.

The ECU monitors inputs from a variety of sensors for the cylinder head temperature, throttle position, fuel-injector pulse time, and engine revs. Other sensors also might include the manifold air pressure, oxygen, and air-inlet temperature. Based on that data, the ECU optimizes the air/fuel mixture hundreds of times per second by determining how long and when the injectors spray fuel into the port. Called the pulse width, the injector's rate of fuel delivery is measured in milliseconds. Mentally compare that system with a carb's mechanical choke and float bowl full of sloshing fuel and you can begin to see why EFI is so much more effective. Of course, you have to pay a lot more for this level of performance. A typical carb-manifold setup for a Chevy V-8 runs less than $500, but figure on $2,500 to $4,000 for a complete EFI system.

Cold-starting is a good example of how an EFI responds to changing conditions. When the ECU senses that the engine's temperature is below a certain level, it enriches the air/fuel mixture to, say, between 11:1 and 12.5:1. Once the engine warms up and is at cruising speed, however, the ECU then leans it out to that sweet spot of 14.7:1. During heavy acceleration, the ECU may drop the level down to 12.5 again. Or if you're driving in the mountains where the air is thin, the ECU can compensate for reduced atmospheric pressure. Getting a carburetor to handle all those changes would be like trying to fit all those cathode-ray tubes under your hood.

One key component of an EFI system is the vehicle's electrical system. Power demands are higher, so a 70-amp alternator is a good idea. All of the connections, particularly the grounds, must be clean and secure. A poor electrical system can be the nemesis of EFI.

Also, EFI requires a fuel-pressure regulator that automatically responds to changes in demand, and injectors need a fuel pump with much tighter tolerances and a fine filter to catch any impurities that might clog a nozzle. Injectors are available in wide range of sizes so they can be tailored to the engine's size, heads and camshaft specs.

In addition, there are three types of injector-firing systems: batch, bank-to-bank and sequential. The batch type is the simplest, hitting all cylinders for every complete rotation of the crankshaft. Bank-to-bank fires half of the cylinders for each half-rotation of the crankshaft. A sequential system pulses each cylinder on an individual basis. Most batch systems can't accommodate changes in altitude, and the sequential system is usually for high-dollar racing applications, so bank-to-bank is generally the best all-around way to go.

Aftermarket companies offer two basic types of ECUs: programmable and non-programmable. The advantage of a programmable type is that it allows the system to be set up for a specific application using either an internal flash programming or a removable chip. The auto manufacturers' computers have an advantage in terms of the millions of dollars of research behind them, but hot rodders usually prefer aftermarket units that can be programmed more quickly with a laptop to make changes at the track, or to adapt the engine to forced induction from a turbo or supercharger or nitrous oxide.

Another amazing aspect of EFI is that an engine can be tuned by phone! Using a computer modem, a technician can tap into the ECU and check the readouts and fuel curves, and make adjustments as needed in the programming of the fuel curves. Imagine explaining that to our computer pioneer.

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