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(CHECK ENGINE LIGHT) Catalyst system efficiency below threshold

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Old Jan 22, 2011, 11:52 AM
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(CHECK ENGINE LIGHT) Catalyst system efficiency below threshold

Ok so i got a check engine light on and i went over to AAP. They did a scan for me and told me it was the Catalyst system efficiency below threshold, and the computer did not say if it was bank one or two. SO I have 3 possibility's. Bad CAT, Or One of the O2 sensors is bad. Anyone out there experience this yet? I have a 3'' exhaust setup all the way back. But stock headers. I did not setup u this exhaust system so i know little about it. But anyone out there with any info, PLZ help.
Old Jan 22, 2011, 11:54 AM
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Test pipe? If so you need to do a search and read how to fix it. Sweet mother of mary this post is right under yours lol. I cant make this **** up!

https://www.evolutionm.net/forums/ev...-question.html
Old Jan 22, 2011, 12:13 PM
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here's a video to make it easier.

http://www.youtube.com/watch?v=qoAkDnwP60c
Old Jan 22, 2011, 12:20 PM
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Get an O2 extender for the rear 02, like this for example...

http://cgi.ebay.com/ebaymotors/O2-ex...Q5fCarQ5fParts


The reason for the Cat eff is that the difference from front and rear 02 is not much.
Old Jan 22, 2011, 12:26 PM
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Or you could go to Autozone or Advance Auto and get 2 spark plugs anti-foulers. Those did the job for me.
Old Jan 22, 2011, 12:47 PM
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Originally Posted by dacib
Or you could go to Autozone or Advance Auto and get 2 spark plugs anti-foulers. Those did the job for me.

Be more descriptive? How does it work
Old Jan 22, 2011, 12:48 PM
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Originally Posted by 4RETECH
Get an O2 extender for the rear 02, like this for example...

http://cgi.ebay.com/ebaymotors/O2-extender-Oxygen-Spacer-HHO-Wideband-Dry-Cell-Sensor-_W0QQcmdZViewItemQQhashZitem4aa7d05ccaQQitemZ32064 3030218QQptZRaceQ5fCarQ5fParts


The reason for the Cat eff is that the difference from front and rear 02 is not much.
You think this is my problem? Why do you say to get this.
Old Jan 22, 2011, 12:53 PM
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Here are detailed instructions:

https://www.evolutionm.net/forums/ev...cel-light.html
Old Jan 22, 2011, 01:02 PM
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Thank you Dacib, Im still excepting all other ideas or experiences.
Old Jan 22, 2011, 01:30 PM
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I run a test pipe and two spark plug anti foulers drilled the top one out. works great no check engine light. and the test pipe gave me the extra spot for my wideband 02
Old Jan 22, 2011, 01:33 PM
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Ok here is the picture of the O2 on the test pipe. ( SO is this my problem?) I was wondering is it damaging anything since its saying check engine. Is it maybe running to lean or rich.
Attached Thumbnails (CHECK ENGINE LIGHT) Catalyst system efficiency below threshold-photo-2-.jpg  
Old Jan 22, 2011, 01:56 PM
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Originally Posted by Uaevolancer
Ok here is the picture of the O2 on the test pipe. ( SO is this my problem?) I was wondering is it damaging anything since its saying check engine. Is it maybe running to lean or rich.
I don't know but the picture looks like the two wires are cut,fuzzy picture though
Old Jan 22, 2011, 02:21 PM
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Ill double check that right now
Old Jan 22, 2011, 03:40 PM
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The reason it did not show what bank on the code results, is because a inline-4 only has one bank.

I firmly believe that the test-pipe is causing your CEL to come on.
If you get the sensor out of the main stream exhaust flow, it will think the catalytic converter (that isn't there) is doing it's job.

My hollowed cat causes the same problem, but I'm too lazy to do anything about it, instead I just use my scanner to clear the code when it comes up.

Good luck!
Old Jan 23, 2011, 12:55 PM
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So you all believe i have a 50/50 chance of fix this problem.


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