Joe, my understanding is this. Forst of all the sensor has NOTHING to do with the voltages you see, unless they are actually 0-1 volt like a 2008 and 2009 bike. Then the MOCO put a bias voltage across the whole system so that nowadays we read in the 1700s or what ever. This has NOTHING to do with the sensor.
It has been MY understanding that this was done to quell noise being generated into the 0-1vdc system. Think of it this way, if noise generates a spike of 200mv, that becomes 20% effect in fueling... on a 01-vdc system. On a system with an added 1000mv bias volatge applied to the grounds... that 200mv becomes around a few % points change.. See? If this was, as Bob says for EPA reasons... maybe so, because this would help keep fueling in line while in closed loop. It would eliminate wild swings in fuel control while the fuel warbles going down the road. I would tend to be fairly certain a 10% variance, induced by noise in the sensor wiring, could force the ECM to lose its mind and lose control of fueling. Same with the car guys, Joe... its about some metal rubbing and making a charge that influences the final readings inside of the ECM. If this would be a 'tight' electrical circuit with ground drains and all of that, we most likely wouldn't need this offset, but with a simple two wire O2 sensor (the other wires are for the heaters) all of the crap can INDUCE voltages into that two wire circuit. See? Another ting to consider is the 'how' the noise can enter the system. with a 0-1vdc signal, this is an ANALOG signal, and NOT digital. It will make a sine wave on a scope and not a flat line going across like pure single voltage DC. Sine wave looks like a heart beat on a monitor, or surely you have seen an AC sine wave? Anyways, going down the road, when the bikes is in closed loop, that sine wave comes MIGHTY close to zero volts. If and when it touches zero volts, this becomes like AC voltage and not DC. (AC voltage is NOT necessarily a sine wave, but IS a sine wave that hits zero volts at zero potential) This AC volatge is half of what we generate and use everyday in our homes and business, but this WILL screw up fuel control's warble dance. Teeny bit of noise inline and the ZERO portion of the graph can get lifted enough to make the low points ground, and hence AC voltages. With the 1000mv bias in place, the whole sine wave is lifted from zero volts by 100%, so even is the sensor WERE to get to zero volts at the sensor, inside of the ECM it will NEVER get close to touching true zero and this makes it impossible for the voltages to become AC like.
Out at the sensors? The voltages are still the same as in 2007 with the 18mm sensors. This voltage is applied inside of the ECM as a noise offset. AT least, this is what I understand to be happening.
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Topic: O2 Sensor Output (mv) compared to measured AFR (Read 153999 times)