I could use a little o/2 voltage tutorial

[devind]

Could someone please give me a little tutorial on reading and understanding o/2 sensor voltage? (I am running a 3 wire heated O/2 sensor)

The problem I am having is with a $OD tune. I am having issues primarily with idle. I can have the engine completely warmed up to operating temp then unhook the PCM to clear any BLM learning. Restart it let it go into closed loop and have a perfect 128 BLM at idle. Then drive it for a while then when I come to a stop and let it idle the BLMs will drop down to 120. There are other time when the BLMs will take a unexplained swing for no reason and seems to stay there like it is locked occasionally. (Also I am running a Vortec TBI GM performance intake which is heated with the coolant so intake temps should be consistent too)

I was talking with Dave and he mentioned he had had experience with O/2 sensors start going bad and do this before. He suggested I watch the O/2 sensor voltage on the monitor and look for any discrepancies such as the voltage staying high or low.

I have noticed when you let off of the gas while decelerating it will stay high then go back to a peak and valley pattern. However mine seems to sometime stay in the high or low range for no apparent reason sometimes.

So as the title says I could use a little o/2 voltage tutorial. Data is only as good as the person looking at it is able to understand it. So if anyone would care to share a little on the subject I would sure appreciate it.

[delcowizzid]

post a log file and adx

[lionelhutz]

To keep it simple, the O2 goes below 0.5V when the engine is lean and it goes above 0.5V when the engine is running rich. The switching point is a lambda of 1.0 (complete combustion) or what people call an AFR of 14.7:1. During times like decel and wide open throttle, the ECM will go open loop and pick a lower or higher AFR which drives the sensor to a continuous high or low voltage. Remember, an AFR below 14.7 is rich which is a high voltage and an AFR above 14.7 is lean which is a low voltage.

When closed loop, the ECM continuously varies the fuel. It will first begin to remove a little fuel until the O2 voltage goes low. Then, it will add a little fuel until the O2 voltage goes rich. I suggest you look up the explanation of a PI or PID control loop to get a better idea of what it's doing.

[ony]

might have 1 spark plug not working like it should?

[devind]

To keep it simple, the O2 goes below 0.5V when the engine is lean and it goes above 0.5V when the engine is running rich. The switching point is a lambda of 1.0 (complete combustion) or what people call an AFR of 14.7:1. During times like decel and wide open throttle, the ECM will go open loop and pick a lower or higher AFR which drives the sensor to a continuous high or low voltage. Remember, an AFR below 14.7 is rich which is a high voltage and an AFR above 14.7 is lean which is a low voltage.

When closed loop, the ECM continuously varies the fuel. It will first begin to remove a little fuel until the O2 voltage goes low. Then, it will add a little fuel until the O2 voltage goes rich. I suggest you look up the explanation of a PI or PID control loop to get a better idea of what it's doing.


might have 1 spark plug not working like it should?

Thanks for the responses!