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O2 sensor readings


Guest jimmyk
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'89 Reatta--What are the correct readings for the O2 sensor when using the CRT diag? Mine seem to fluctuate even with a steady throttle opening. Readings are 12 to 80 with a steady speed/throttle.

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There is no single correct reading, but it is designed to indicate in a range. The .80v would be on the rich side and the .12v is lean. That information is sent to the ECM which adjusts the injector pulse width to try to bring the reading to the stoichiometric value of approx. .45v. The more active the sensor, the better. Cross counts is the indication of how often the O2 sensor changes from rich to lean and back. The system is constantly adjusting on the fly as it should.

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I thought that the changes would be more linear. The reading range I understand, but the changes are nearly instantaneous, changing from 12 to 80 5 times or so per second. Are those type of readings normal?

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Repeating the same numbers over and over doesn't sound like what I normally see, although a somewhat large swing from high to low sounds familiar. I don't know if it has anything to do with the update rate of the display and/or ECM or not? As long as it swings back and forth around the theoretical optimum, I look more at the cross counts. What do the Integrator and Block Learn readings look like? They both should settle at approx. 128 if everything is operating in harmony, but some variation above and below is pretty normal and I believe the amount of ethanol in the fuel will make the BLM trend a little higher. It also needs to be after the engine is fully warmed up. How is the fuel mileage?

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