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Unread 02-25-2012, 06:28 PM   #1
defcon_klaxon
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'95 YJ not passing smog, high NOx...help!

hi guys,

my '95 yj (2.5L, no mods) is not passing smog. specifically, the NOx emissions are way too high, and the CO emissions are right on the border of passing. i've been doing a lot of reading and research into fixes, and after the 2nd check today i'm still failing. wondering if you guys could help.

here's what i've done so far:

1. tune up (distributor cap and rotor, spark plugs, wires, oil change)
2. seafoam treatment (through vacuum line off brake booster, half a bottle)
3. found two exhaust leaks before catalytic converter, had them welded
4. new fuel filter (to make sure adequate fuel was flowing)
5. put a couple gallons of 91 octane in before test, drove around to make sure system was at full running temperature

at this point, i'm basically wondering what else i can do...i know some guys have changed their catalytic converter and that seems to help, but so far as i know a cat doesn't affect NOx emissions at all, so why would that help? o should mention that PO (my buddy) replaced catalytic converter back like 5-7 years ago, so it's not the stock unit. also, haven't checked o2 sensor but in theory wouldn't the jeep throw a CEL and a code if the o2 sensor was too rich or lean? or maybe i can't rely on the system to verify o2 sensor operation?

i will say that when i had the exhaust shop look for and fix exhaust leaks, they said my manifold was supposedly cracked (though i don't see a crack anywhere). also, the forward most and rear most studs for the exhaust manifold are missing...that being said, she passed smog with flying colors two years ago when i bought her and those studs were missing then too.

basically i've spent a couple hundred damn dollars on this so far with some very big ticket items on the horizon...besides taking it to a shop to have them diagnose it, is there anything else i can do?

btw, i am aware that this model of jeep does NOT have egr, so that's not something i can look into.

thanks for any suggestions you can provide, this is driving me crazy and i just don't trust that a cat is going to fix my problems unless someone can describe why NOx would be reduced with a new cat.

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Unread 02-25-2012, 06:51 PM   #2
Collin89Sahara
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Make sure the correct test was performed.
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Unread 02-25-2012, 07:17 PM   #3
Flood
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You need a new catalytic converter, they do reduce NOx. I went through the same thing a few months ago.
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Unread 02-25-2012, 07:21 PM   #4
defcon_klaxon
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Quote:
Originally Posted by Flood View Post
You need a new catalytic converter, they do reduce NOx. I went through the same thing a few months ago.
I was just reading about how "three way" converters do reduce NOx, something I've never heard about until now. With that basically being the only other thing to try, looks like I'm gonna have to head down to the exhaust shop tomorrow.
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Unread 02-26-2012, 01:40 AM   #5
judgevalor
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Get the California cat and you'll be sure to pass. I had the Nox issue myself and had to upgrade to the new California model to pass. It passed with flying colors after I changed it out.
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Unread 02-27-2012, 08:08 PM   #6
laybackman
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If you are running too lean you will end up with high engine temps and possibly high NOx temps. I also had high NOx and swapped in a new three way cat converter and then passed with flying colors.

If you ran around with a leak in the exhaust system somewhere before the O2 sensor you would have been runnning a false lean engine. The air leak fools the O2 sensor and it in turn tries to repair the false lean condition by dumping a bunch of fuel into this engine. Any gas that gets to the cat converter can kill it.
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Unread 02-28-2012, 04:55 AM   #7
wetwilly2
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hc=ignition
co=fuel
nox=heat
check your egr system
maybe open up the gap a little on the plugs
you also could have a lazy o2, but usually wont effect nox
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Unread 02-28-2012, 06:12 AM   #8
laybackman
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Quote:
Originally Posted by wetwilly2 View Post
hc=ignition
co=fuel
nox=heat
check your egr system
maybe open up the gap a little on the plugs
you also could have a lazy o2, but usually wont effect nox
There is no EGR system on his year YJ. The three way cat converter makes it unecessary. I still think the OP's cat converter got contaminated with raw fuel due to an exhuast leak which caused the false lean condition that caused the raw gas to be dumped into his exhaust which killed his cat converter which was already pretty tired.
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Unread 02-28-2012, 07:47 AM   #9
CJ7dreamer
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Bump up the ignition timing, that will help alot.
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Unread 02-28-2012, 07:54 AM   #10
laybackman
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Originally Posted by CJ7dreamer View Post
Bump up the ignition timing, that will help alot.
The timing is controller by the brain so he can't do that...
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Unread 02-28-2012, 08:10 AM   #11
Old4X
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Quote:
Originally Posted by CJ7dreamer View Post
Bump up the ignition timing, that will help alot.

Even if he could, advancing the timing increases NOX.
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Unread 02-28-2012, 10:11 AM   #12
CJ7dreamer
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Quote:
Originally Posted by Old4X

Even if he could, advancing the timing increases NOX.
That has not been my experience...... That's exactly what my buddy who runs a smog shop told me to do and it brought the NOX down to within specs on my kid's car and it worked for me......

I hate emissions testing, that's why I ended up getting a 71 jeepster commando.....
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Unread 03-13-2012, 08:54 PM   #13
defcon_klaxon
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Just wanted to post in case others find this thread looking for help...I was finally able to pass the dumb CA smog test. I ended up having to replace the catalytic converter, plus the o2 sensor.

Basically I did all the tune up/sea fom/easy stuff, still had really bad numbers. New catalytic converter cleaned up my HC and CO, plus my NOx at 15mph...at 25mph, it was still twice as high as was allowable. The last thing I could do was the o2 sensor so I changed it. Sure enough, the next time I tested it passed.

I did find a few exhaust leaks before the cat, so I had a muffler shop weld them closed. This didn't help my numbers at all.

since my years of YJ don't have EGR, if you're seeing high NOx it's probably your cat and/or o2 sensor...some guys have said they pass after sea foam treatments and using high octane fuel, but none of that stuff will be helpful if your cat is dead.
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