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Old 01-19-2014, 11:05 AM   #1
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94 yj failed smog for high oxides of nitrogen

He smog guy said I failed because of high oxides of nitrogen and he thinks it's running lean, translation please?

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Old 01-19-2014, 12:12 PM   #2
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NOx = Created from HIGH combustion chamber temperatures.
Lean = more air then required for a correct mixture (14.7:1 which is what the CO2 should be on your report Higher then 14.7 = lean, lower = rich or a bad cat)

Also the result of a LEAN condition (Vacuum leak, Biased O2, plugged injector, low fuel pressure)

An exhaust leak BEFORE the cat converter can result in O2 entering the exhaust and flooding the front half of the cat, effectively disabling the NOx reduction bed. Our Jeeps are popular for this, the header pipe cracks where the pipes join.

Carbon on the pistons creating higher compression (resulting in hotter burn cycle).

NOx can also be the result of a non functioning EGR valve (if you had a 4.2L, you would have one), but dont worry, your 94 doesnt have this.

Please scan/post your ENTIRE emissions report.

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Old 01-20-2014, 08:21 PM   #3
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That's the form, this stuff for me is like trying to read ancient Egyptian lol
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Old 01-20-2014, 08:46 PM   #4
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Check and repari ALL/ANY exhaust leaks before the cat.

Your CO2 is low, your O2 is High

Your cat is either bad, or he tested it COLD, which i kind of doubt because NOx is created by high temps....
Some shops recommend an O2 sensor with a cat, I normally say run it after the cat, if it needs the O2, it will fail again.
But since im the one running the smog, Im biased, it might be good insurance to replace the O2 anyways....

And One more thing, you didnt post the entire report, there is information at the bottom I use that didnt get posted, it might SEEM irrelevant to you, but it actually means something to me.
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Old 01-20-2014, 10:44 PM   #5
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Alright here is the full report
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Old 02-26-2014, 08:48 PM   #6
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I also failed my emissions due to NOx being too high on my Jeep YJ 1988 4.2L and I had one question for those who could help. My Jeep has the Motorcraft mc2150 carb, and I'm not sure if that eliminates the EGR valve I'm looking for.
Does anyone have a picture of what the EGR valve looks like on this engine because I need to know where mine is or if it is even present due to my MC2150 carb???

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