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Tech Notes: |
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O2 Sensors |
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Every new car, and most cars produced after
1980, have an oxygen sensor. The sensor is part of the emissions control
system and feeds data to the engine management computer. The goal of the
sensor is to help the engine run as efficiently as possible and also to
produce as few emissions as possible.
A gasoline engine burns gasoline in the presence of oxygen. It turns out
that there is a particular ratio of air and gasoline that is "perfect,"
and that ratio is 14.7:1 (different fuels have different perfect ratios --
the ratio depends on the amount of hydrogen and carbon found in a given
amount of fuel). If there is less air than this perfect ratio, then there
will be fuel left over after combustion. This is called a rich mixture.
Rich mixtures are bad because the unburned fuel creates pollution. If
there is more air than this perfect ratio, then there is excess oxygen.
This is called a lean mixture. A lean mixture tends to produce more
nitrogen-oxide pollutants, and, in some cases, it can cause poor
performance and even engine damage.
The oxygen sensor is positioned in the exhaust pipe and can detect rich
and lean mixtures. The mechanism in most sensors involves a chemical
reaction that generates a voltage. The engine's computer looks at the
voltage to determine if the mixture is rich or lean, and adjusts the
amount of fuel entering the engine accordingly. The reason why the engine
needs the oxygen sensor is because the amount of oxygen that the engine
can pull in depends on all sorts of things, such as the altitude, the
temperature of the air, the temperature of the engine, the barometric
pressure, the load on the engine, etc.
When the oxygen sensor fails, the computer can no longer sense the
air/fuel ratio, so it ends up guessing. Your car performs poorly and uses
more fuel than it needs to. And just because an oxygen sensor is failed,
or already has failed, does not mean the "check engine" light will
automatically come on. |
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