High NOx, failed smog test

Blue Squirrel

Blue Squirrel

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Aug 7, 2017
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Los Angeles, CA, United States
Hello Everyone,
I have a 1999 Jeep Wrangler that couldn't pass the California smog test this year. When it failed the first time a month ago for high NOx, my mechanic told me the catalytic converter was worn out and needed to be replaced. So I had a new cat installed. My Jeep has Federal emissions but because I live in California, I bought a California-approved cat. I got the Jeep retested but failed again. Took it to a shop that was recommended by a couple of people, the new shop found the exhaust manifold was cracked so we replaced it. They also replaced the O2 sensors. The shop retested but NOx was still too high. They installed new fuel injectors (?) and retested but since it failed again, they put back my old ones because it didn't look like the new ones made a difference. The technician also reset the adaptations by disconnecting the battery. After all this, smog test failed again. I was able to get a one-time waiver from the State BAR Referee because I had already spent over the monetary threshold in emissions-related repairs but this means I have two years to figure out what's wrong with my Jeep because it MUST pass the next smog test or else I would need to retire the jeep or sell it to someone out of state where smog tests are not required to register the vehicle. I'm out of my wits end and no one could seem to figure out what else could be wrong with my Jeep. It's running great, no black smoke or anything like that. My Jeep doesn't have an EGR system in it so that couldn't be the problem either. Please help. Thank you very much in advance.
 
Is the Jeep fully warmed up and running at 210 degrees during the tests? It won't pass if someone screwed up and replaced the correct and required 195 degree thermostat with a lower temperature 165 or 180 degree thermostat.
 
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I don't know how a CA emission test is administered but I'm going to assume that they sample exhaust gases with a tailpipe probe. Do they run the vehicle on a dyno roller and do a simulated road test?

Here in AZ my 94 Dakota had to be tested on the rollers since it was pre OBD2. It failed the emission test several years ago due to hi NOX. I requested and received the computer trace of my test (it looks like an EKG). From this trace I determined that I had a faulty EGR valve. I had zero drivability issues and had noticed no change in MPG.

By looking at the printout I could see that NOX only exceeded the threshold at only one specific place during the test cycle. This one point was when the throttle was allowed to snap closed during the road load portion of the emission test. This condition is one of the times when your EGR valve is most active.

I had to insist that the test technician not reset the computer before printing my copy of the computer trace. If I had moved out of his bay and then tried to get a copy it would have been too late.
 
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I just reread your post. Do I understand that there is no EGR system on your engine at all? If this correct please disregard my post.
 
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Jerry Bransford said:
Is the Jeep fully warmed up and running at 210 degrees during the tests? It won't pass if someone screwed up and replaced the correct and required 195 degree thermostat with a lower temperature 165 or 180 degree thermostat.
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Hi Jerry. The last test I had, I drove the Jeep for about 80 miles on the freeway and went straight to the smog shop and I didn't turn it off at all while I was waiting for my turn.
 
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jgaz said:
I don't know how a CA emission test is administered but I'm going to assume that they sample exhaust gases with a tailpipe probe. Do they run the vehicle on a dyno roller and do a simulated road test?

Here in AZ my 94 Dakota had to be tested on the rollers since it was pre OBD2. It failed the emission test several years ago due to hi NOX. I requested and received the computer trace of my test (it looks like an EKG). From this trace I determined that I had a faulty EGR valve. I had zero drivability issues and had noticed no change in MPG.

By looking at the printout I could see that NOX only exceeded the threshold at only one specific place during the test cycle. This one point was when the throttle was allowed to snap closed during the road load portion of the emission test. This condition is one of the times when your EGR valve is most active.

I had to insist that the test technician not reset the computer before printing my copy of the computer trace. If I had moved out of his bay and then tried to get a copy it would have been too late.
Click to expand...
Yup, they did a tailpipe probe and dyno roller.
 
What's interesting to mention was that my shop who replaced the cracked exhaust manifold and o2 sensors thinks I bought a subpar/defective cat. I got a catco 940106 universal fit that's applicable to my jeep and corresponding Executive Order #. In California, aftermarket cat converters need to be covered by an Executive Order which means the state certified that the cat converter can be used/installed in your specific vehicle. If you install a cat that's not meant for your car, you could fail the visual test during your smog test and the technician will fail you indicating your emissions system is "tampered", unless you have stamp from BAR Referee who inspected and approved installation. That's in California.
Anyway, back to the cat I have, my mechanic thinks that if I use a different cat, which is made for a 1998 Jeep Wrangler, my jeep might pass because this cat has a larger honeycomb surface material than the one I have currently. I asked him how sure he was, he said 75%. I'm willing to give this one a try, but I'm hesitating because 1) he's not sure by doing this my jeep will pass 2) I will shell out $750-$900 to do this on top of the $1300 I already spent relating to this issue just to find out if it would pass. If it doesn't, what then?
 
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Jerry Bransford said:
Ok but does your engine run at 210 when warmed up or at a lower temp?
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Not sure. How can I tell? Sorry, I'm a newbie and don't really know much about cars. Just learning as I go and from what people tell me. I'm assuming I can tell by the temp gauge in the dash?
When I took the Jeep to the BAR Referee, I was told that one of their functions was to make sure the smog test was performed correctly. The BAR website says that the referees can perform tests that regular smog shops can't. People who dispute the smog test results they got from their local smog shop go to the referee to get the "official" result. My jeep was smogged by the referee and it failed. In fact, on their smog test, my Jeep was rated a Gross Poluter :( I'm assuming the referee knew how to run the smog test correctly, i.e. ran it at the right temp.
 
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Jerry Bransford said:
Look at the lower right-most temperature gauge on your instrument cluster once the engine is fully warmed up.
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Hi Jerry, sorry it took a couple of days to get back to you. The temp my Jeep runs on is at 210. I took a pic of it this afternoon while I was stopped at a red light. The needle is always in the middle when I'm driving. This is my normal temp.
By any chance, do you know of a mechanic/shop who could possibly help me? I called Pacific Jeep in Hermosa Beach and they told me to just sell the Jeep.
 
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Any follow up on this? I have the exact same issue on a 1999 XJ federal model. Just put in a new magnaflow 3-way ca approved cat at a respected muffler shop and failed with super high nox (1600).
 
Sometimes caused by a really hot combustion chamber... possible causes are a lean fuel mixture, the engine is running too hot, or a carboned-up engine from driving too conservatively, Does your engine ever ping. knock, or rattle from pre-detonation?
 
Dang, sorry you're having so much trouble. I just went through this about a month ago, failed the first test but passed the 2nd. I have a 98 with 180k miles on it. The engine is tired, knocks and spits some white smoke. I replaced the Cat and O2 sensors. Just for giggles I also threw in some Engine Restore which actually reduced some of the knock (still there) and now it doesn't spew white smoke. I passed the test.
 
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