Some questions about a failed smog test - JeepForum.com

 
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post #1 of 3 Old 10-18-2013, 10:57 AM Thread Starter
tkwok
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1995 YJ Wrangler 
 
Join Date: Aug 2006
Location: california
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Some questions about a failed smog test

Recently, my YJ failed the NO portion (25mph) of the smog test. My measured reading was 804. The MAX. is 542. The cat. is only 3 years old and I put in a new NGK O2 sensor about 2-1/2 years ago. I took my jeep back to the muffler shop where the cat. was purchased and had them inspect it. Sure enough, the cat. had failed. They informed me that my jeep was running rich and that contributed to the failure of the cat. A new Walker cat. was installed and I put in a new set of Champion copper plugs. I took it back to get it re-tested. This time, it passed but it barely squeaked by. The new measured NO reading at 25MPH is 534. Everything else in the test results are within spec.

Can someone give me some explanations as to why I am getting such high reading even with a new cat.? Are there other factors involved here? I don't want to have other components that are contributing to the failure of this new cat. a few years later.

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post #2 of 3 Old 10-18-2013, 11:48 AM
Siva283
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1995 YJ Wrangler 
 
Join Date: May 2011
Location: Falling Waters
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Because its running rich. Check for codes before anything else. Also inspect your exhaust manifold for cracks and missing or loose bolts.

1995 YJ. 2 inch BDS Spring lift. 1 inch shackle lift. 1.25 inch JKS Body Lift 33x12.5x15's. Engo 10,000 pound winch.

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post #3 of 3 Old 10-18-2013, 11:51 AM
Que89YJ
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1989 YJ Wrangler 
 
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Location: Detroit
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Nox high is a lean burn. O2 failure is almost always going to cause it to run rich. If you are running lean the 2 biggest issues is a bad air density from the air temp sensor or low fuel pressure(Since you are at 25 it could be the vacuum line for the pressure regulator). Check the air temp sensor just with a meter and see what the resistance is. Fuel pressure is 31 psi idle, 39 with the vaccum line pulled, and then with the vacuum line reconnect shut it down and it should hold pressure above 20 psi for longer then 20 minutes.
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