running lean
 

I'm running a catless header and I've been throwing a code p2096, post catalyst fuel trim system too lean bank 1. Any idea of risks for this? I know if its too lean I can blow my motor so I don't want any smart ass answers. I'm looking for actual technical discussion as to what is actually too lean and I will provide logs of Afr commanded and measured with corresponding rpm. Is there anything else I should be logging like load or anything else?

Did you run any sort of oxygen sensor spacer? I ran into this code too. So I took the spacer out and got po420 code. Long story short: watch your fuel trims. As long as you are +/- 5% from 0 you are fine. However CEL will affect you traction control systems. So spending time with spacers and washers to get the perfect spot in between where you will get lean code from being too far out, or p0420 code from being too close I've got over 7k on my Catless header with no ill effects and fuel trims +\- 5%

I have this weird 90% thing on my downstream sensor that was given to me when I bought the exhaust.

Basic question, is the car tuned for no cats?

No tune.

ECU is not getting an expected rear o2 sensor reading because of the catless header.

The rear o2 sensor is used for the catalyst monitor (which most people are aware of) but it's also used to adjust the reading of the front o2 sensor in cruise operation. It accounts for degradation in the front o2 sensor.

Which sensor is bank 1 and which is bank 2? If bank 1 is the downstream that explains everything, if bank 1 is the sensor before the cat I'll have some questions. The obvious answer is to have the car tuned, but I have other things that thousand dollars needs to go to, on the other hand if it is running too lean it might be worth it to do a tune first.

We only have bank 1. Sensor 1 is up stream aka primary O2 aka front sensor aka pre cat. Sensor 2 is downstream aka secondary O2 aka rear sensor aka post cat.

The lean code probably indicates sensor 2 is a bit too far from the stream of exhaust gas or has too small of an opening.

It was too far. I removed the spacer, probably gonna get a running rich code. Thanks for the help.

or cat inefficiency code P0420. Vibrant sells one you can tweak, it has 3 different orifice inserts IIRC.

How long were you running the spacer before the code first came up? I've been running an angled o2 sensor on my Borla UEL header for 2,000km now. 2 track days and a lot of highway running with the cruise control on, no CEL so far.

It comes on pretty quick. Could you post a pic of how yours is mounted please?

Here you go

http://i374.photobucket.com/albums/o...ps8a13de1e.jpg

http://i374.photobucket.com/albums/o...ps1036cdda.jpg

That helps, but do you have a close up so I can determine the angle in relation to the exhaust flow?