Dave,
>
>10% ethanol is all I can get here in Minnesota for the past 3 or so
>years, so you can be pretty certain that the use of ethanol in your
>vehicle didn't damage anything. Your decrease in mileage with that
>fuel is as expected. (BTU per gallon of ethanol is lower than regular >gasoline)
>
>When was the last time you replaced the oxygen sensor? If never, and
>the car has more than 60,000 miles on it, you might as well just >replace the sensors.
>
>The oxygen sensor in a production vehicle is typically considered a
>"narrow band" oxygen sensor. These sensors are only able to signal
>how close to "perfect" the oxygen level is. So one voltage will be
>too rich, the other voltage means too lean. The engine computer
>monitors the oxygen sensor and adjusts the fuel ratio when in closed
>loop many times a second.
>
>When the sensor tells the EEC that the engine is running rich, the EEC
>pulls back fuel timing to decrease the amount of fuel injected. Then
>when the sensor says things are lean, the EEC adds more fuel. The EEC
>is never able to do better than add a little fuel till it's too rich,
>then take a little fuel out until it's too lean. This flip and flop
>of the engine management system is keyed directly to how fast the
>oxygen sensor can itself sense too rich and too lean.
>
>As oxygen sensor is constructed with a platinum coating. Over time
>this coating becomes damaged or oxidized and hinders levels at which
>the sensor will respond to rich or lean conditions. This causes the
>engine computer to get the engine too rich, before it's told it's
>rich, and too lean, before it's told it's lean. This has a noticeable
>impact on fuel economy of your engine. Older OBDI computers often
>could only fail an oxygen sensor if the sensor gave signals off scale,
>or didn't ever change. Current generation OBDII engines use dual
>oxygen sensors and they have response timings they expect the sensors
>to perform within. Once they stop performing within those timings,
>the check engine light will be triggered.
>
>The point of all of this is, if you haven't replaced your oxygen
>sensor in a number of years and a number of miles, there is no
>question your care will perform better if it is replaced.
Nice comment Mike :)
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