Catalytic converters

[justin]

I have a 1999 4-Runner Limited. I put a K & N airfilter charger on. Truck runs great but I have encountered the "Check Engine Light." Saying the engine is running lean and the first o2 sensor might be to blame. I have decided to try and put my Borla exhaust on to see what will happen...So...Trying to put a Borla exhaust (p/n 14659) on it but I have encountered a second catalytic converter! Do I really need this second one? I had a '96 Limited and it only had one cat. (with two o2 sensors). I live in CT. I know they put these on for CA emissions at one point...
It does have two oxygen sensors. One in front of the first cat and other after the second cat.
HELP.
Am I making sense?

Justin

[WristPin]

ok boys are you interested in fixing the truck?

find your O2 sensor. Then visit a mufller shop, like meineke. have them back pressure test the catylictic converter. they can determine if there is a clog. this clog can lead to(if not addressed) future leaks with in the engine.
expect to pay $40- $85 per O2 sensor. and no more than $40 for the back pressure test.
the Cats prices range from shop to shop....

class dismissed

[justin]

Thanks! I'll check it out...

[Jukelemon]

Justin:

The first O2 sensor sets up many many fuel/air specs. The second o2 sensor indicates a failure in the cats i.e. clog etc. If you are getting primary (1st) o2 sensor failure, it is probably a bad sensor. The K and N filter really does nothing in terms of affecting the programmed air/fuel mixture from the ECM i.e. it is set to deliver more POTENTIAL air but nothing more. Point being, I bet it is a failing sensor.

Just my .02.

[justin]

Cool. I really appreciate all the input.
The check engine light first went on right after I put the K & N on. That is why I am questioning the amount of air intake vs. fuel mixture. I did bring it to Auto Zone for a reading and the diag. said it was the first 02 sensor reading a lean mixture...
By the way, I am going to put a Borla system on this truck and I have two catalytic converters (CA emissions version?). Do I really need both or can I get rid of the second one for this system to properly fit?

[Jukelemon]

I really have never heard of an air filter causing those issues. I have heard of headers doing so but not a filter. I have changed many many filters back and forth. As well, I have run no filter before becasue of a mouse that destroyed mine and havign to go to the store and buy one. Never an issue with the CEL.

In terms of your questions about the dual versus single cat, I would think it DOES matter because of this logic. The CA emissions are different and therefore probably have different ECU programming. Likewise, I know that a CA O2 sensor is NOT the same as a Fed O2 sensor. I ran into this when I replaced my sensor i.e. picking the right one. So, I would tend to think, in terms of emissions, you need to keep with the std. Fed. single cat set up.