I could use a little o/2 voltage tutorial

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.

post a log file and adx

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?

Quote:

---

Originally Posted by 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.

---

Quote:

---

Originally Posted by ony

might have 1 spark plug not working like it should?

---

Thanks for the responses!