o2 sensor nightmare

Joshua T · Jul 25, 2016

Let me keep this as quick & simple as possible.

About 3 weeks ago a bought a wifi OBD2 scan tool. I connected it to the Torque app for android. Watching my short term fuel trim while using o2 sensor it sky rocketed to positve 25.4. Now in thinking that i may have a bad o2 sensor i shut the car off & unplug the front o2. Started the car with it unplugged & wouldnt you know it... The STFT while using o2 sensor was still maxed at 25.4???

Any ideas? Is that what it is supposed to do or do you think that there may be a short in the ground somewhere on the o2 sensor wire harness??

Car specs:
98 eclipse GST spyder 2.0

Lou98GSX · Jul 25, 2016

Sounds like you have a vacuum leak .

Joshua T · Jul 25, 2016

Okay i did a cold start test. The STFT was perfect between -5 & positive 5. O2 voltage was going up & down fine. Then after warn up i took a drive. 1 mile down the road the O2 voltage wont go past 0.0 voltts & at that very second the CEL comes on with p0170.. Bad O2?

dsmrestorator · Jul 25, 2016

Vacuum leak is possible but if you can remove the 02 sensor and examine it you may notice that it looks really charred, if that's the case, good chance your 02 is no good. But looking for a vac leak is easy and free. The leak may appear once the engine gets up to temp.

Lou98GSX · Jul 25, 2016

If you have a code for an o2 sensor then i would change it cause if you had a vacuum leak you would get fuel system lean code .

Joshua T · Jul 26, 2016

So I replaced the o2 sensor today & wouldnt you know it... I was able to go 127 miles on $13. Before I replaced it I was getting about 85-90 miles on $20?!?!

Before:
Using o2: STFT 25.4 all the time after warm up.

After:
Using o2: STFT 3.2 to -8.9

I would recommend that everyone grab an obd2 wifi scanner & use Torque to see what your o2 voltage is. I got mine for $5 on ebay.

So my conclusion is that I am getting 27mpg vs getting 13mpg max before.. All because my o2 would stop sending voltage information to the ECU.

Thanks again for all the great comments!

krygods · Jul 26, 2016

Link to the scan tool your talking about?

dsmrestorator · Jul 26, 2016

Glad to see it all worked out for you. :thumb:

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o2 sensor nightmare

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