What are the symptoms of a bad O2 sensor?

[NHRA Super Gas]

Curious what everyone has seen when their sensor is known bad. I just ordered 3 new denso's, should be here by the weekend. AC today.

I'm asking because it seems like my 02mv at cruise and even idle can be all over the map....120, 400, 730,550, that type of thing. I suppose a perfect 780 constantly is tough to come by.

 

[RUQWKNF27]

that seems normal to me .. mine are always all over the place.. its when they are not you need to worry... also when you seems to be using a lot more gas will be the symtom of one going bad!!

 

[Louie L.]

What you r describing is normal at crusie. The O2 is switching back and forth in close loop mode.. If the swings were slow or none the O2 would be bad.

Simptoms of a bad O2 at WOT are lean conditions even you have the correct supporting hardware,pump ,inj, maf ect.. Popping and studdering. A bad O2 can also cause poor idle.

780 mv is needed at WOT only and that number is just a reference. Some cars need more than that... This is where a wide band helps.

 

[TurboBuRick]

O2 millivolts jumping around is normal. That means its working.
You are looking for 780 mv in 3rd gear wot with no knock.
When the scanmaster records data you can look at the o2 and what gear you were in.
Thats where you shold be looking for your 780mv
But like louie said, some cars need more.

 

[Terry_H]

Curious what everyone has seen when their sensor is known bad. I just ordered 3 new denso's, should be here by the weekend. AC today.

I'm asking because it seems like my 02mv at cruise and even idle can be all over the map....120, 400, 730,550, that type of thing. I suppose a perfect 780 constantly is tough to come by.

What you are hoping for is what you see when the sensor is bad. You want fast constant hunting. If you see a lull, the sensor is bad. It can also throw a code.

 

[NHRA Super Gas]

Thanks all. I'm going to replace the 02 anyway, in anticipation of my first track day next month. I was asking because on the Turbotweak site, it says 02 at idle should be 780-820. It seems like I'm there sometimes, and like I said bouncing around a lot as well.