Ok i understand the 02 serves the A/F to help keep it at stoich 14.7/1. this helps the cat/conv maintain proper emishions as well.( i dont have a cat). from what i heard it sends a signal in open loop but the ECU does not use it or disregards. i further heard that it is at .45mv(my reccolection) at stoich but actually moves the ratio above and below that 14.7 to keep cat/conv happy. does this mean it moves the actual A/F to say 14.5 and then moves to 14.9 ? is this close on accuracy? in my aldl stream i see volts moving around a bit. is that because the ecu expects the ration not at 14.7 but above and below? at steady cruise it seems to drift on /around .450. i believe it is staying in one fuel/spark cell but cant be sure of that. also when AE or PE invoked it obviously changes per my visual aldl stream. i really dont spend a lot of time reading it as there are traffic issues. i am installing a WB02 next week and trying to get a better grasp as what is all going on. if anyone can expand or correct this please do. 7747.

 

ttt

 

The ecm AVERAGES 14.7:1.
It spends a certain amount of time richer them Stoich, and leaner then stoich to keep the converter happy. A cat won't work correctly at a fixed 14.7. There's an incredible amount of fudging of numbers to get the chemistry correct for doing all this. In the case of Ford they use a series of powertrain dynos, and huge industrial strenght WB, and gas analyse to get a calibration to do what they want, and the oem O2 sensor is just a cheap devise to maintain what they've found to work.

Using closed loop is a good way for a new guy to get the jest of what's going on, and how to get there. Once you get into things for a while, you'll see how to rethink things as you go, and possibly make changes in what you want to do. Initially getting all the lil quirks, in the VE and timing tables are a plate full.

 

Basically you can think of an O2 sensor as a SWITCH!
It generates a voltage based on a difference between exhaust oxygen and the oxygen outside of the sensor (some use the oxygen in the wires of the sensor, some have openings in the back of the sensor).
Lean = Excess exhaust Oxygen = low O2 differential = low voltage.
Rich = No Oxygen (all burnt by fuel) = high O2 differential = high voltage.
When warm it is almost impossible for a (properly functioning) sensor to spend any time at 450 mV. I mean even in open loop and in lab like conditions, still isn't gonna happen on a real engine.
That switchover point has some hysteresis built into it in the form of response time, where it is easier to switch from high to low, than from low to high, or vise versa, depending on manufacturer specs.
The ECU outputs a bias voltage of 450 mV when the sensor is cold, and uses that voltage to determine the resistance or impedence of the sensor, which is megaohms when cold, and is a voltage generator when warm.
When warm, and in closed loop, the ECU responds oppositely to the sensor, so that when lean (low voltage), it richens, and when rich (high voltage), it leans. There are several techniques that can be used to bias this richer or leaner, such as holding it rich a moment, or by taking larger steps in one direction, or jumping back more at sensor crossover. This will look like a sawtooth pattern of some sort that at an average is somewhere close to 14.7:1 A/F. Manufacturers go to great lengths to optimize this for their particular catalyst, which does require the switching to perform correctly. Without the switching the efficiency drops really quickly, because the cats need to store fuel (CO and HC), then get some air to burn it, and store some air, then get some fuel to burn and then store, and back and forth. If held at a constant A/F, even 14.7, it'll get cold quick.

For those trying to get actual A/F from the sensor, and believing it's accurate to the tenth of an A/F, please don't. Sensors age. Aging will bring the max voltage down. A cheap wideband will convince you it was worth it in seconds. Even if it's a trade-off, new hood vs WB, WB wins. If building a new engine, put WB in the shopping cart as part of the build cost (and a timing light if you don't have one).

Enough preaching,
Later,

 

that is what i needed. thanx.