Lean O2 Mystery

[steddy]

Ok, I'm running out of options as to what is making the car throw an SES light up. '96 Firebird, 3800 series II, modified, no cat, no EGR, dyno tuned. I have been chasing this rabit for what seems like an eternity this season. Bank 2 Sensor 1 is throwing both a P0151 and P0154 code (Lean and low voltage).

Anyway, checked the motor for leaks with a hose to isolate any noises better. Found that at Bank 1, the EGR blockoff plate had been leaking, so I welded that closed, thus, no leak there. Headers aren't loose or leaking (at the heads or y-pipe, no vacuum leaks (well, that I could find) and yet the problem is still there. It also has a subtle surge that occurs when I take it out of gear. The only thing I can guess (which I really hate to do at this point) is that the O2 sensor may be bad (not the stock GM unit), judging from the A/F ratio being good, but the PCM sensing a lean condition, making it richen the mix up some to compensate, but only at the lean bank. Is there anything that I may have missed? I'd hate to go through the dealer, put in another sensor and find out that the problem is still there.

[Mogobs30th]

Re: Lean O2 Mystery

Did you tune out the EGR?

[steddy]

Re: Lean O2 Mystery

Did you tune out the EGR?

Yes, as well as the post CAT sensor.

[Mogobs30th]

Re: Lean O2 Mystery

Could be the O2 sensor, but what do you have in place for one if it's not the stock GM unit?

[steddy]

Re: Lean O2 Mystery

I believe it's a Standard Products version (supplier is Advance Auto for this particular place). Had some trouble with HO2s a while back and at the time, the place that had a decent scan tool warranteed them. Of course, after changing out roughly 6 of them since, this could be pointing to the problem. :twak: me for going with warranty stuff. Could just be a second rate sensor, and after changing over and over, what good is a warranty anyway? Other than pointing me in all sorts of directions needlessly. Yeah, I'll put stock back in and see what happens with it.

[Hib Halverson]

Re: Lean O2 Mystery

You said that the AFR was good but the sensor is reading way lean.

How did you determine the air-fuel on that bank is ok?

[steddy]

Re: Lean O2 Mystery

Snap-On diagnostic computer. Showed all other parameters were working fine, but the bank 2 sensor was reading a low reference voltage (almost no movement within the parameters that bank 1 was in, small changes/spikes, compared to the sweeping changes of bank 1). Also went old school and used a hose to listen to various areas of that side of the engine, from the exhaust to injectors and intake and found no vacuum leaks or unusual noises, O-rings weren't leaking at the injectors and the headers are torqued well. Also tight at the Y-pipe connection and all vacuum hoses are connected and solid.

[Hib Halverson]

Re: Lean O2 Mystery

I'd replace the sensor.

IMO, the best sensors are made by Denso, next best are OE GM.