Running Rich?

[Silver Snake]

I recently went to the dyno and got low numbers, including my A/F, which was off the chart rich (below 10). I was told to reset the PCM and come back the following day. When I came back the next day my numbers (including A/F) were good. Before I reset the PCM I was seeing about 11-12 MPG and the rear bumper was always covered with soot. It has now been about a month and I think I might be running rich again. I have not gone back to the dyno, but my bumper is still sooty and I am still getting 11-12 MPG.

Today I went out for a little drive and when I came back I decided to check my plugs...they looked just fine. Am I worried over nothing? Is 11-12 MPG normal and is the sooty action normal?

What should I check for? O2 sensor? Something else??

Thanks
Mark

 

[Qualitywires.com]

Any mods?

I would definely check the O2's (More the fronts than the rears).

Map sensor gone bad?

Any codes?

 

[Silver Snake]

How do you "check" the 02's? Do you mean just replace them? Is there a way to determine otherwise? Also, how do I check the MAP sensor?

The car is bone stock.

Mark

 

[Ulysses]

Mark,

Isn't this the second time you have had to reest the PCM? It's most likely not the O2s. You can check them by having Jason hook it up to a DRB.

 

[Silver Snake]

Mark,

Isn't this the second time you have had to reest the PCM? It's most likely not the O2s. You can check them by having Jason hook it up to a DRB.

No. This is still referring to the first (and only) time I reset. I did this awhile back during the dyno day weekend at WCV. Between then and now, I am noticing the soot on the rear bumper and the poor MPG.

The thing that confuses me is that my spark plugs look just fine even right after a little driving.

So, if it is not my O2's what could be causing the problem?
Mark

 

[Ulysses]

I'm not saying that it isn't the O2s, it's just unlikely it is. Let's assume you have your O2s checked and they are okay.

The next thing you have to check is your AF/fuel trim. If it says you're running rich then you have to think about it a bit.

This means that POSSIBLY, the O2 sensor is sensing MORE unburnt oxygen than it should. That points to a possible exhaust leak before or near the sensor, or an injector that is stuck open. When listened to with a mechanic's stethescope, the injector should pulse at a steady rythm.

Your map sensor could be faulty in the sense thay it is sensing more air than is really available, but it is harder to diagnose.