I Know You Heard This Before But...cel Question

[BlexusGS]

I need help and advice. A while back I was getting a CEL and its code was PO171 (engine bank #1 too lean). I went to my mechanic and he was hesitant to work on my car because of my air intake. He mentioned that it was probably my O2 sensor. I told him that I'de rather him work on it than the Lexus Dealer because of their high price. He said he would only work on it if I sign something stating that if the CEL does not go out he cannot be held responsible; I agreed because I didn't know if my intake was the cause of the problem. Anyway, he replaced the O2 sensor and guess what... the damn CEL came on again. I drove back to the mechanic and they checked the code; still PO171 (engine bank #1 too lean). What the hell??? He told me to clean out my MAF (and be delicate about it). I searched on this forum and found suggestions to spray rubbing alcohol and use Q-tips carefully; so I did and also reset my ECU. About 5 miles into driving the CEL comes on again!!! What can this be??? Can my MAF be bad, how can I tell? Also, how would I know if my custom ram air setup to my intake isn't the real culprit. I don't want to replace the MAF or the "other" O2 sensor (there are 2 O2 sensors regarding A/F on the GS) just to find out that I'm changing out good parts. Please advise!!!

[SRK]

For what it's worth, here is my interpretation of your symptoms.

First, O2 sensors sense oxygen, which seams obvious, but they DONT sense lean. They sense high oxygen content and the computer interprets that as lean, and as the single O2 is reporting a high oxygen content then it is bank specific. So that means the mass meter can't be at fault. It also means that the original O2 was doing it's job, reporting a condition that is out of range. Therefore, what is causing the exhaust gas on one bank to have excess oxygen? A partial misfire can do that, like a bad plug. A busted exhaust manifold gasket, or a bad injector seal can do that. Keep in mind that an O2 sensor doesn't see a misfire as "rich" because it doesn't see the unburned fuel - it sees "lean" because it reads the oxygen not consumed in normal combustion.

I also can't see how the air filter can cause the problem, although perhaps others have experience with them doing this.

Chances are the engine will have to be scanned in real time to observe the code being set - a power graphing multi-meter is the kind of device that will do that. A simple code reader will not give the data required. And that will prevent you from hanging a bunch of parts that will not fix the problem.

I hope this helps a bit.

[darrylg33]

Air is getting in there somewhere, that is the long and short of it. You need to find out where it's getting in....period...could be a simple gasket or O-ring not seated properly, these cars are extremely sensitive and the computers pick up any little thing that is out of the normal operating range. There is a smoke test that can be performed to see where air is getting in but it should be performed by someone who knows what they are doing and how to do it. Search here and maybe you can find someone who has done one succesfully...good luck!

[BlexusGS]

Thanks guys...I am prinitng out your posts so I can show my mechanic. Maybe you guys touched on something that they haven't thought of. I'll let you guys know what happens.

Thanks,

Nick

[InspiredGS]

i noticed that you put "custom CAI" in your sig.. the CEL light is probably due to the cold air section of your intake pipe.. my guess is that your cel light problem with go away once you remove the custom cold air piping and return it back into a short ram... another way you can go to fix that cel is to get an AFC... example: Apex-i S-AFC-II.. that and some dyno tuning should also fix your problem.. GL

[BlexusGS]

Thanks tlx I am going to have a reputable shop supply, install and tune the S-AFC. Before that I will remove the extension and see if the CEL goes away. If it does ...then my MAF is OK and the S-AFC and dyno tune will cure all.