A/F Sensors vs O2 Sensor PCM behavior

Mr. ScannerDanner,

I have been researching A/F sensors. From your videos, other videos, and books, I have learned that in the heart of every A/F sensor is our beloved O2 sensor. When I learned that, it made total sense to me. Why not leverage a sensor that we all know works. In addition, since the PCM is controlling/managing the A/F Sensor, the PCM can respond quickly to exhaust stream composition changes.

But that isn't what I'm writing about.

What I'm writing about is the Short Term O2s oscillation. As a programming geek, I totally get why the PCM uses the STFT to stay around 14.7:1 by zig zagging across it. This is a simple algorithm to ensure you're right on the mark.

So, in many write ups and videos, it is stated that the oscillation also allows the catalytic convertor to get oxygen which is used in the chemical process it undergoes. But, when a PCM leverages an A/F sensor, I don't see this oscillation. So, how is the catalytic converter getting its necessary oxygen for it to work efficiently?

So, I guess I have two questions:

Is an A/F PCM system still oscillating? I personally haven't noticed it, but I haven't had a chance to research this across numerous cars.

If not, why not, meaning was the explanation of the catalytic converter needing oxygen not really true?

For me, this is like discussing the tomato sensor. LOL

Did you check out Tyler's thread in the diagnostic tools section? Here's the link

Thanks for the link, Dylan.

GeekDIYMechanic wrote: So, I guess I have two questions:

Is an A/F PCM system still oscillating? I personally haven't noticed it, but I haven't had a chance to research this across numerous cars.

If not, why not, meaning was the explanation of the catalytic converter needing oxygen not really true?

For me, this is like discussing the tomato sensor. LOL

To answer the first question, yes, the A/F ratio sensor DOES still oscillate across stoichiometric. It just happens to do it faster, and with a lower 'amplitude', or amount of correction rich and lean.

Reventon actually asked a very similar question not too long ago, thinking along the same lines you are. I dug up a scan data capture from a 2004 Honda Element, showing the A/F ratio sensor 'switching' at idle. 'AF LAMBDA' is the wideband signal PID we're interested in.



It can be tough to measure due to scaling issues, but observable if you're careful.

Hi,
have a look at this video - or more of these if you're interested -; they are by far the best explanations on A/F sensors I know.