Downstream O2 sensor voltage question, No engine codes

[chilerancher]

For the last year or so was pulling engine codes complaining about cat efficiency. Made sense because the cats were making the death rattle sound and the exhaust smelled increasingly bad. Last week replaced the cat with AP/Eastern 645236 from RockAuto. Codes cleared up and all diagnostics passed so was able to get it to pass Texas inspection.

During my post-fix validation I collected traces from all 4 O2 sensors and saw some unexpected results. What I expected:
* Sensor 1 both banks to dither when in closed loop mode
* Sensor 2 both banks to remain constant around some nominal value

What I observed while closed-loop:
* Sensor 1 both banks dithered as expected at 550 rpm (idle) and at 2000 rpm.
* Sensor 2 bank 1 was constant around .1 V at 550 rpm, climbed to .8 V when accelerating to 2000 rpm then came back down to .1 V at 2000 rpm.
* Sensor 2 bank 2 was constant at .8 V at 550 rpm, didn't change initially after accelerating to 2000 rpm, then eventually meandered down to .1 V at 2000 rpm and then slowly back up to .8 V after returning to idle.

Questions:
1. What is the expected voltage reading for sensor 2?
2. Is the bank 1 sensor 2 "blip" to .8 V while accelerating an issue?
3. Why do bank 1 and bank 2 sensors 2 behave differently? Maybe bank 2 has a heater circuit issue?

 

[Scottydoggs]

scan them o2's in Mv "milla volts" if you can. volts will range from 1 to 8 and just bounce around, not a good way to read them.

both banks will never be 100% the same, but yours looks way off. they wont work right till the engine is up to temp too. why they have a built in heater, to speed the temp of the o2 up so it works faster from dead cold.

easy way to tell if one o2 is lazy or dead and not setting a code is all warmed up got wot, both o2's should lock in at 930 or close to that in Mv. if one drops when wot, or never reaches high 800's its dead.

 

[swathdiver]

Think of your V8 as two 4 cylinder engines with regards to the O2 sensors. The downstream sensors ought to remain fairly constant, if they move like the upstream ones there's a problem and it's usually the catalyst.

If I read your post right, you replaced only one catalytic converter? Which one? Have you driven about 200 miles to break it/them in yet?

 

[chilerancher]

Think of your V8 as two 4 cylinder engines with regards to the O2 sensors. The downstream sensors ought to remain fairly constant, if they move like the upstream ones there's a problem and it's usually the catalyst.

If I read your post right, you replaced only one catalytic converter? Which one? Have you driven about 200 miles to break it/them in yet?

I replace the cats on both banks. https://www.rockauto.com/en/moreinfo.php?pk=1317194&jsn=465
They now have 250 miles on them. All diagnostics have passed and there are no engine codes.
I wish I would have captured O2 traces before I replaced the cats so I had a compare.

 

[swathdiver]

Run another graph after a few more tanks of gas. I think you are fine.