Understand O2 live data (1 Viewer)

[Readhead]

Hi experts,
I have 97 FJZ80 with170000 miles, and trying to figure out if my O2 sensors and the CAT are in a good shape. Looking on both O2 sensors while driving and both seems to operate between 0-0.9v but when in parking in idle rpm, the downstream is around 0.1v +-0.05v and when I increase the rpm to 4000 it is even lower than 0.1v. See pictures. I understand that it should be around 0.45v. I check the back pressure and it is good. The measurements done with hot CAT.
What does it mean? Any thoughts?
BTW,I replaced downstream sensor and got the same results. No error code.

 

[Rusty Marlin]

The FSM has this information and how to interpret the signals.
The FSM is free to download, it's a PDF and very easy to follow.

Resources

forum.ih8mud.com

 

[Readhead]

The FSM has this information and how to interpret the signals.
The FSM is free to download, it's a PDF and very easy to follow.

Resources

forum.ih8mud.com

Thank you for the answer. Actually I had done some homework with the FSA and done the attached test and got the low reading results.
I tried to understand what is wrong but there is no code and no help from the FSM.

 

[Boulder Cruiser]

I just went through some issues with my new 450. I couldn’t get the catalyst monitor to trigger ready. My downstream O2 sensor was following my upstream O2.
I ended up having to replace my cats and within 2 min of driving it triggered my ready monitor. My downstream 02 is basically flat lined now in the middle of upstream curves.
I don’t have a pic of the graph after the cat replacement but this is what the looked like before.

 

[Readhead]

Thank you for sharing!
As far as I understand if the downstream follows the upstream it means that the cat does not do what it supposed to do. Therefore it makes sense to replace or fix the cat.
In my case it is relatively flat but low. I’m not sure what does it mean, maybe I should try to clean the cat with something like cataclean ?
And see if something changes.
Any suggestions?

 

[Rusty Marlin]

Alternating from 0.4 or less to 0.5 or more...
I would say its acting as intended.

 

[Readhead]

Alternating from 0.4 or less to 0.5 or more...
I would say its acting as intended.

It is alternating between 0.02 and 0.08 as you can see in the beginning of the thread. Not in spec

 

[Rusty Marlin]

ah, so I see.

 

[Readhead]

After reading on line, this can be result of a leak in exhaust. I’ll check that.

 

[Readhead]

BTW, I had a hole in the muffler, so I replaced a muffler but this did not solve the O2 reading... Still a mystery...

 

[azusa]

What are using for the graph, is the graphing from the OBD2 connector?

 

[azusa]

BTW, I had a hole in the muffler, so I replaced a muffler but this did not solve the O2 reading... Still a mystery...

Any leaks after the downstream oxygen sensor is not going to affect the readings.

 

[Readhead]

Yes, this is from the OBD2 data. BTW after replacement the muffler, I had checked for other leaks and found a small leak between the front catalytic convertor and the rear one. just between the two sensors. So I assume the air is getting trough the leak and make it leaner in the second o2.