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Post cat o2 sensor ?

 
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ken729
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PostPosted: Sat Oct 09, 2010 8:23 am    Post subject:  Post cat o2 sensor ? Reply with quote

Does anyone know if the post cat o2 sensor in a 3.8l has any impact on air/fuel mix or is it just monitoring cat efficiency? Thanks.
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EMMJAY
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PostPosted: Sat Oct 09, 2010 8:52 am    Post subject:  Re: Post cat o2 sensor ? Reply with quote

ken729 wrote:
Does anyone know if the post cat o2 sensor in a 3.8l has any impact on air/fuel mix or is it just monitoring cat efficiency? Thanks.


when I did the exhaust on my Impala, I was told that it just monitored it, that the motor would not run differently, butt you would have a CEL on, and it is bright and annoying lol...unless u get a PCM and get the code deleted, or of course get a new one.

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EMMJAY, you and I have always had the same taste in cars Hang Head 2
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ken729
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PostPosted: Sat Oct 09, 2010 8:55 am    Post subject:   Reply with quote

Thanks
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nightryder
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PostPosted: Sat Oct 09, 2010 10:07 am    Post subject:   Reply with quote

It has no effect on fueling during normal driving.

However, on some years if you remove it the computer will start dumping fuel to see if it can get a response from the rear O2. Since the rear O2 isn't there it'll run really rich.

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ken729
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PostPosted: Sat Oct 09, 2010 10:29 am    Post subject:   Reply with quote

Thanks so much for your answer. I have a 2000 LS witha 3.8l - any idea if that model year has a post cat o2 that can significantly adjust air/fuel mix?
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bbengineer
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PostPosted: Sat Oct 09, 2010 12:29 pm    Post subject:   Reply with quote

The rear O2 doesn't play into fueling for any year... what nigthryder is pointing out is on some years if the rear O2 isn't present, the PCM attempts to get a reading from it by dumping fuel as a test

Maybe if you describe what you are trying to do or the problem you are having, you will get information pertinent to your issue

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ken729
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PostPosted: Sat Oct 09, 2010 1:51 pm    Post subject:   Reply with quote

I'm just trying to determine what role the post cat o2 plays in air/fuel mix. The reason I'm asking is that I just replaced the pre cat o2 sensor a couple of months ago. I know the pre-cat plays a big role in air/fuel mix. It had 140k with no CEL, my scan tool o2 voltages were fine and the OBD o2 test said it was okay, too. There were no codes on a dealer Tech 2 either. I replaced it anyways because i was at my wits end to figure out a very bad hesitation problem that occured when going from open loop to closed loop. Installing a new o2 solved the problem and my gas mpg went up real nice.. That being said I am now wondering if the post cat o2 should be changed to fine tune the air/fuel mix further - despite the fact it also is not showing any CEL or scan tool voltage problems. If it plays no role, i will just leave it as it is.
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PostPosted: Sat Oct 09, 2010 2:20 pm    Post subject:   Reply with quote

It plays no role... so leave it as is

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ken729
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PostPosted: Sat Oct 09, 2010 2:22 pm    Post subject:   Reply with quote

Thanks
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