Curiosity Question: O2 Sensor Pre Vs. Post Cat

[rick s 2]

The way I understand it: The O2 sensors after the cats are always (during easy driving) striving to maintain the 14.7 : 1 AFR. As the AFR goes above and below the 14.7, it tells the computer, "A little richer. Now, I little leaner. Now, a little richer." And that up-and-down adjustment reading is what we are seeing on our AFR gauges.

We always mount our aftermarket AFR wideband sensor bung before the cat. And that constant up-and-down adjustment is why our AFR meter's display is constantly changing: 14.7, 14.6, 14.5, 14.6, 14.7, 14.8, 14.9, etc.

I know we are not overly concerned about the AFR reading during normal driving. When we get into part throttle and WOT boost is when the AFR tables change, and that reading becomes critical.

But for the only reason being: To have a more steady 14.7 display reading. Not that constantly cycling 14.7 ish display, why don't we mount the wideband sensor after the cat? Is there a big delay in that "after the cats" reading? Or, does the after-the-cat reading change just as fast when we push the pedal into the power tables?

I'm just curious.

[Hemi31 194]

The sensors before the cats are maintaining 14.7. After the cats are making sure your cats are doing their job.

[Speedy 247]

What Erik said.

Furthermore, the system CONSTANTLY adjusts. It will never just be dead nuts 14.7 for any real length of time on these cars. I've never seen it set rock steady on any car for that matter.

[rick s 2]

Thanks guys.

[fnkychkn 4]

As well as monitoring catalyst efficiency, the downstream O2 sensor signal values are also used to calculate upstream O2 sensor goal voltage.

sent from the fnkyfone