adding a resistor to the o2 input wire - Page 2 - Fuelly Forums

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Old 03-13-2008, 09:04 PM   #11
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Originally Posted by kamesama980 View Post
yes, the o2 sensor is used to adjust the whole fuel map over time, NOT for instantaneous response.
i dunno, it seems like it does it pretty fast, cause I disconnect my battery (which resets the computer) to install eeprom chips in my computer with new tunes and when I have the o2 enabled the a/f quickly goes to 14.7 or really close to it.

maybe its just my car, cause I know there such a thing as drivability issues after resetting a ecu or disconnecting battery. not that I've really seen, but it is in repair info.
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Old 03-16-2008, 05:27 PM   #12
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is there not such a device or what??

I'm going to school for auto tech. and one of the books has a chart in it showing that you get better mileage with a leaner mixture. from what I've read it seems that 14.7 is just for emissions.

no, wait, why the hell would a leaner mixture cause higher emissions???
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Old 04-09-2008, 10:37 AM   #13
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i

no, wait, why the hell would a leaner mixture cause higher emissions???
Higher NOX.
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Old 04-09-2008, 11:43 AM   #14
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Ummm backwards thinking alert...

The sensor reading lean does not mean the car will run lean. It means the ECU will add fuel to get it richer again. So putting any resistance in there will actually make it run richer.

You wanna fake it out and run lean as hell, get a 1.5V alkaline battery and a 2 silicon diodes, connect the 2 diodes in series to the +ve of the battery and run that and a lead off the negative to the O2 sensor inputs on the ECU... But the fact that the O2 is not cycling either side of stochio or "switching" will probably clue the ECU something is wrong and it will fault it.
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Old 04-09-2008, 08:38 PM   #15
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A resistor would be a bad choice of component anyway... Resistors limit current, not voltage. The O2 sensor produces very little current, so you would need to use a very high value in order to see a voltage drop across the resistor.

Even if you do manage to adjust the voltage somewhat, it would actually make very little difference in the air/fuel ratio. If you look at the response curve of a typical lambda (narrow band) sensor, it's flat up until something like 14.5:1, then takes a steep dive, ending up flat again by around 15:1. You simply can't tell much from the sensor output beyond that range of air/fuel ratios. So, even if you find a way to offset the sensor voltage, you still won't be able to go beyond that range of AFR readings... You would be feeding the ECU your false sensor readings without actually knowing what the oxygen content of the exhaust is. If you wanted an air/fuel ratio of 17:1, you would be shooting in the dark... Your sensor would simply be telling you the air/fuel ratio is somewhere over 15:1. Your signal tweaking circuit wouldn't know when to switch from 0 to 1 volts without a real reading from the exhaust stream.

What you need is a sensor that will give you readings for a wider range of air/fuel ratios - A wide-band sensor. Your best bet here is to use a wide band controller with an adjustable simulated narrow-band output. That would simply let you tell the controller to put that 14.5-15.0:1 window at 16.5-17 AFRs. That's well within the wide-band's operating range, so you'll be producing the fake signal based on actual readings from the exhaust stream. When the oxygen content in the exhaust shows the AFR at 17:1, the wide-band will actually read it as 17:1 and flip that 0 to 1 volt simulated output, where as the circuit using a narrow-band sensor would simply read "something over 15:1" and have no clue other than that.
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