Hello. I was playin around with a scan tool and notice that at idle the O2 sensor flips back and forth from lean to rich. When I get on the gas it runs lean tho. Just curiuos why and what I can do. There was no load on the engine while I was playing around too, so I don't know if that had anything to do with the readings... Thanks!

- Tom

 

The "rich, lean, rich, lean) is normal. Its showing that the O2 sensor is transitioning between rich and lean. A healthy O2 sensor will switch back and forth from about 100mV to 900mV with 450 mV being the middle. An O2 sensor that is dead usually hangs around 450 mV. That part is normal.

However, when you "get on it" it should not read "lean". When the ECM goes into "power enrichment" mode, it will add lots of fuel and the scantool should read rich. For one reason or another, your running lean under load.

 

thanks...will investigate the lean then

 

When you say there was no load, do you mean you were just reving in neutral?
On my car, under actual load (driving) I get a rich condition in P/E- as it should. but just reving it with no load, it will jump up to rich with the first rev and go lean when you hold the engine at a steady rpm.
Is this what yours is doing also? I've never had any problems yet, and mine has been like this for a few years.
I assumed it was because without load, there is more vaccum and the regulator isn't increasing psi like it normally would under load/decreasing vaccum thus causing a lean condition.?
Can anyone confirm or correct this.

 

yes, that is what i meant by no load. I just had it in park/nuetral. I didnt notice if it jumped to rich when i first tapped the gas but it at steady RPM it was lean, and when i let off after it bein steady it jumped to rich . I could always check my plugs. What are some reasons why it might run lean? thanks.

- Tom

 

OK, I missed the whole "No load" part. Sounds like you don't have a problem. The best thing to do is take off at WOT and monitor your O2 sensor mV. At WOT (in Power Enrichment) it shoult jump to 800-900mV and STAY there untill you let off the gas. Simply revving in nuetral won't do this.

 

will do, thank you