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Dr. Graham Edgar developed the octane rating system in 1926 to measure the ability of a fuel to burn cleanly. Higher-octane gasoline burns in a way that pushes the piston down smoothly during the power stroke. Lower-octane fuel burns too rapidly, and that can make a knocking or pinging sound in the cylinder, which can harm the engine. You maximize fuel economy and get the cleanest emissions by using the octane rating recommended in your car's owner manual.
Eighty-seven and 90 are the normal ratings for everyday unleaded gasoline
Unfortunately, misinformed car owners often switch to higher-octane gas in an attempt to rid their car of foul-smelling exhaust fumes or as a "treat" for the engine.
Don't be fooled!
When you refuel with a gasoline rated higher than your vehicle requires, you are wasting your money and sending unburned fuel into the emissions system, damaging key components and risking more rotten-egg smells.



Fuel Injection

Fuel injectors controls the flow of fuel to the pistons.

Vehicles before 1990, this procedure was carried out by the carburetors, which had changed very little through the decades. All engines used the same principles. As fuel regulations tightened, requiring greater fuel efficiency and cleaner burning fuel, new ways had to be found to meet the more stringent standards.

Starting in the late 1970s, a few cars used fuel-injection systems. And all were making the move to computer control. Around the mid-1980s, the last of the computer-controlled carburetors were phased out, and manufacturers shifted to electronic fuel injection on all vehicles.

These early fuel-injection systems provided an air/fuel mixture much the way a carburetor did. It was a similar system in that fuel was atomized into one carburetor-like opening and was called a "central fuel-injection system" (or a "throttle-body system"). One significant difference between these early fuel-injection systems and a carburetor system was that the fuel injector no longer relied on engine vacuum to pull fuel into the air stream and suck it into the engine.

Fuel injectors inject fuel under pressure. And in the process a finer atomization (mist) is produced, hence better fuel burn, more complete combustion, reduced emissions, and greater economy. Coupled with catalytic converters, early electronic fuel injectors were efficient enough to meet EPA emissions regulations during the 1980s.

As emissions standards tightened again in the 199Os, newer, superior fuel-delivery systems were required, and in the process cars took another step forward in engine efficiency. The newer systems were called multiport injection systems. These systems place an injector on each cylinder, meaning fuel is directly injected into the cylinder, yielding a finer spray of fuel, more complete combustion, reduced emissions, and greater economy.

Recall what you now know about the internal combustion engine. 

With the carburetor system, when the air intake valve opens, the downward moving piston draws in the air/fuel mixture from the carburetor. The same held true with throttle-body injection. But with multiport injection, a fuel injector sits next to the intake valve of each cylinder. On the downward movement of the piston, only air enters through the intake valve. The atomized fuel is injected separately into the space created by the piston's downward motion.

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