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Reged: 08/16/01
Posts: 5810
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Re: Could someone explain to me some A/F Gauge Stu new
#1298050 (Re: hsoverma) 08/11/06 01:39 AM

Here is my best shot at "explaining" why a narrow and wideband are different without any science to complicate the issue.

Wideband has a voltage range from ~approx 0-2volts. You can search for the voltage scale.

The regular narrow sensor works form 0-1volt and they aren't calibrated so that you can read them directly. That is because the stoichiometric A/F ratio is such a narrow portion of the sensor voltage that the pcm can't read with enough resolution from it to determine the actual stoiciometric A/F, even if it were constant. The way around it is to oscillate the A/F from rich-to-lean really fast so that the O2 sensor voltage goes above and below the stoichiometric point, and then the pcm will figure out the average from that.

Think about balancing a broom stick straight up, it will not stay so it starts to fall left you give it a little nudge and it goes over the top and starts to fall right then you give it a little nudge back. You can't determine the exact point that will balance the broom stick upright as it is so small so you just keep tipping it back and forth very close to the apex.
This is exactly what the pcm does with the air fuel ratio only it is changing the injector pulsewidth to make it rich-lean and try to "balance" the sensor at the stoichiometric point.

Widebands don't work that way, they output a constant voltage based on amount of oxygen in the exhaust. They cost a lot more and need special electronics to run the heater and read the results in a format you can use. They are also much more sensitive to water in the exhaust and under/overtemp. The narrow bands are cheaper and more durable, but give them time and they may improve wideband O2 technology to the point where they will be cheap enough for regular cars.

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