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O2 sensor readings

qwerty247

NAXJA Forum User
Location
uk
Hi,

i am trying to figure out if my O2 sensors are working ok on my 97 xj?

does anyone know what the correct readings should be for them?


thanks
 
I'm curious too. What about "slugish" 02 sensors? Will those still trip a code in the ECU?

I've been watching ebay, and you can get cheap (even OEM) sensors and parts there.
 
Jeeppowr said:
I'm curious too. What about "sluggish" 02 sensors? Will those still trip a code in the ECU?

I've been watching ebay, and you can get cheap (even OEM) sensors and parts there.

Yes if their sluggish enough to cause a problem.
 
So that means, if you don't have a engine code, you have a good sensor? Or can they be almost "sluggish enough" to rob some milage and still not throw an error code? In other words, is the MIL indicator a RELIABLE way to troubleshoot 02 sensor problems?

I've been very confused by so many people claiming to replace your 02 sensor preventitively if it's "old". Of course definitions of old vary from 1 yr to 100K, or "whenever your gas milage starts getting really bad."

To get us back on track (and avoid jacking this thread) I checked my OEM shop manual for trouble codes and voltages:

Various MIL lamp 02 sensor trouble codes: P0030, P0036, P0130-P0161 (these include two for sensor showing "sluggish response"), P1195-P1197.

The manual goes on to say that the 02S (oxygen sensor) can fail in any or all of the following ways: slow response rate, reduced output voltage, dynamic shift, shorted or open circuit(s). On my XJ (1999 model), I have two 02 sensors (one before, and one after the cat). Your '97 should be the same, but I'm not sure.

The output voltage range of the 02S vary from 0 to 1 volt, and can be anywhere in between based on detected oxygen concentration. As the sensor starts to malfunction, it can take longer to detect changes. To detect a shift in the A/F mixture, the sensor must detect a change within a threshold value; a malfunctioning sensor could have difficulty changing beyond this value.

To me, the last statement seems to imply that the computer may have trouble detecting a bad sensor, but I really don't have a clue!

Some other tidbits: Operating temp for the 02S is 300-350 degrees F, and the sensor generates a voltage INVERSELY proportional to the amount of oxygen detected in the exhaust, and are VERY temperature sensitive. The 02S heater element must be tested to insure it's attaining proper temperature.

The downstream sensor copies the voltages of the upstream sensor, with the only difference being the time lag between the two [question: does this mean they are the SAME type sensor in different locations? or are the two different types (non interchangable) sensors?].

It can take 2 failures in a row to trip the MIL, and 3 good trips in a row to reset it.

After all that, I think I'll stick to just replacing my with the low milage ones I bought off of ebay, just because I have 120k+ on my original ones. It actually seems easier than testing them (considering my MIL isn't on), and it only cost me $35 shipped...

Hope this helps!
 
The reason for the different information is mainly because of differences in years being discussed. The 97 and up has sensors that double check the sensors. You have up stream sensors that control the engine and can effect mileage, but you have down stream sensors the test the up stream ones.
We talk a lot about Renix engines and they have not of this double check stuff
 
its seems more complicated than i thought...

no fault codes have come up, so i guess i better just leave it then?

i am only getting 10mpg out of it, was getting around 16mpg a couple of weeks ago and now suddenly down to 10mpg

just trying to work out what it could be?

done the plugs, leads, filter etc and still the same
 
The only way to check what reabings the 02 sensor is putting out when the vehicle is running is with a scan tool.Cost for the tool alone is several hundred $$$ then you need the softwear to run the tool also $$$.
Much cheaper to just change the sensor.
Wayne
 
qwerty247 said:
its seems more complicated than i thought...

no fault codes have come up, so i guess i better just leave it then?

i am only getting 10mpg out of it, was getting around 16mpg a couple of weeks ago and now suddenly down to 10mpg

just trying to work out what it could be?

done the plugs, leads, filter etc and still the same

Have you checked for a plugged CAT, a cracked exaust manafold or air leak?

Also temp sensors could cause no code but low mileage.
 
I have the scan tool and the software...

interesting you mention the cat because thinking about it now it was after i changed the cat...

what do you mean by plugged?

also i keep hearing about check air leaks but dont know where to check for them?

the manifold is ok.

thanks for you help
 
By plugged I mean that it's restricting flow for some reason.
You can test it with a pressure gauge before the CAT you want to see 7# or less, it there more you have a restriction in the exaust.
Air leaks are most often caused by a crack causing air to be drawn in before the O2 sensor. This trickes the sensor to add more fuel because it see a lean mix when it is not.

If it's running good though I would look at the Temp sensors first, MAT and CTS.
 
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