CamaroX84

I finally got my laptop up and going using the Moates software for my new engine. I was taking some readings tonight, and I was going down a straight stretch of road, and with a constant 1700 RPM, constant throttle, and with a constant MAP reading, the O2 sensor was all over the place. Here is an example of a stretch of O2 sensor readings, with everything constant:
177, 314, 354, 371, 601, 769, 601, 756, 712, 685, 296, 172, 663, 857
These readings took place a little over 1.5 seconds. The BLMs were pretty constant (between 124 and 126). Is the O2 sensor supposed to fluctuate this much?? If not, what can I do to fix it? Thanks in advance.

91L98Z28

Absolutely normal and is a GOOD thing. It means the feedback loop (closed loop) monitoring of the exhaust is working.

In a nutsheel, here's what an O2 sensor does. When the AFR is leaner than 14.7:1, the O2 volts will be somewhere below 0.450mV. How much lower doesn't matter, it doesn't mean anything. And when the AFR is richer than 14.7:1, the O2 volts will be somewhere above 0.450mV, again how much higher doesn't matter as it doesn't mean anything.

So, you're driving down the road, and say the motor is running 14.65:1 (richer than stoich). O2 sensor reads somewhere above 0.450mV. The computer reads this, and pulls a tiny bit of fuel out. After a few milliseconds, the computer reads the O2 sensor again. this time it reads somewhere below 0.450mV, indicating lean (perhaps 14.75:1). Computer adds a tiny bit of fuel, and a few milliseconds reads it again.... and this loop continues.

The O2 sensor can NOT read 14.7:1! It's not possible. But it CAN read "more than 14.7:1" and "less than 14.7:1". And the computer constantly and rapidly flips it back and forth so that it averages 14.7:1.

If all that's confusing, think of it this way. You have a light bulb, and a switch. The light bulb is currently on (RICH). You apply a little pressure to the switch, a little more, a little more, and CLICK the switch flips and the light goes out (LEAN). Now you apply a little pressure, a little more pressure to the switch...CLICK light bulb comes back on (rich again) and the process repeats. Now if you imagine this happening fast enough (supefast motion!), the light will appear to be lit dimly, instead of just "on or off". That's what the O2 sensor is doing. RAPIDLY going rich/lean. And if half the time you are slightly rich, and half the time you are slightly lean, then on average you are perfect!