Thanks! I assume if the engine runs lean there is no negative to this, unless it is way lean? The thing is, how would you know (measure) if it is too lean? I guess I need to learn more about what happens when the ratio is lean and far too lean. I also assume the PCM can be tuned to compensate for the SLP CAI & Whisper lid I have...

I should get a fuel pressure test to see if my fuel pump is keeping up...

PS: found some useful tips here:
http://www.automotivehelper.com/topic144238.htm
I read that some of the most common fault codes (DTC's) pertain to fuel trim (rich mixture, lean mixture, etc.) -- which could mean they matter more to emissions purposes than anything else...

Anyone delved further into this Pandora's Box? ;-)

 

After plugs, wires, injector and coil replacement also due to Cylinder 5 misfire, I still have a System Too Lean Bank 1 & 2. The aforementioned replacements helped just for a few months...

 

Ok when an oxygen sensor fails it reads an extremely high oxygen reading the car willcompensate by dumpin excess fuel into your air to fuel mixture causing the car to run extremely rich.... however due the the high reading of oxygen the car believes its running lean.... your mainly hurting your fuel economy but replace the 02 sensors and make sure if car calls for heated o2 sensor to get the correct one good luck

 

Something to look into. I assume JUST the ones PRIOR to the Cat, correct? If O2 sensor(s) are bad, shouldn't I get some catalytic efficiency code as well?

 

not always

 

Ok, but are you talking about the sensors before or after the cat? Just before, right?
I forget, I think there are just two in the V6, right?

 

The biggest problem I have now is trying to get the check engine light to come on when I'm taking the car to the shop. I can reset the code, and it's sometimes hard to get it to come back. However, over the weekend I got it to come back 5 times, this morning -- nothing. Maybe it only happens when the car is warmed up.

Taking to shop like I did last time does no good if they tell you they couldn't get the code(s) to come back on...

 

Something else to consider if you are you still getting misfire codes. A misfire will make the O2 sensor see a lean condition. The O2 sensor looks for oxygen content, it really does not care about anything else. So when the cylinder misfires it dumps raw fuel and air into the exhaust. The O2 sensor only reacts to all the oxygen in the exhaust, but does not care about raw fuel. The O2 sensor sees all that excess oxygen as the result of a lean mixture. The PCM reacts by enriching the fuel mixture, making things worse.

 

It's an O2 sensor... If you're misfiring, fix that first and then reset all codes. Then if the lean condition shows back up, O2 sensor is bad. Bank 1 is your driver side bank of cylinders. Bank 2 would be the passenger side. Sensor 1 is the sensor before the cat on the downpipe. Sensor 2 would be after the cat.

Hopefully that helps ya

 

Interesting, but I haven't got any misfire codes yet since the coil pack that covers cylinder 5 was replaced months ago, just the two lean codes. The codes are reproducible, but intermittent.

Perhaps there could be mild misfires that are not yet detected by the computer? I imagine I will get more codes as time goes on and things deteriorate further...