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Unread 04-04-2013, 07:56 PM   #1
Prubear
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1994 YJ Wrangler 
 
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Need help with CA smog!!! High NOX readings

I'm having problems passing smog in my 94 wrangler. The motor is out of a 94 cherokee. 4.0 liter

I just got my smog check done today and failed due to high NOX readings at the 15MPH test the max is 522 and i measured at 663, the 25MPH test max is 542 and I measured 654...

I had my exhaust replaced 2 years ago from the engine back in order to pass the smog then.

Any ideas on what I can do to fix it???

Thanks in advance for any help.

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Unread 04-04-2013, 08:00 PM   #2
Xpress
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Is your EGR functioning? High NOx is usually caused from running too lean, the EGR takes some of your un-burnt exhaust fumes and sends it back into the intake to richen up the mixture and lower the NOx output.

Double check your timing as well.
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Unread 04-04-2013, 08:03 PM   #3
Prubear
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Quote:
Originally Posted by Xpress View Post
Is your EGR functioning? High NOx is usually caused from running too lean, the EGR takes some of your un-burnt exhaust fumes and sends it back into the intake to richen up the mixture and lower the NOx output.

Double check your timing as well.
I thought that there wasn't an EGR valve on this year? It's just a hose isn't it?
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Unread 04-04-2013, 08:36 PM   #4
NonRubicon
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From what I understand the 4.0 doesn't have an EGR valve.

High NOx is usually due to high combustion chamber temps as the final cause. The thing is to find out why you are getting high combustion temps.
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Unread 04-04-2013, 08:40 PM   #5
SeanB95YJ
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got any relatives in AZ or NV? (or anywhere else for that matter?) just register it at their address. California is ridiculous
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Unread 04-04-2013, 08:48 PM   #6
Prubear
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Quote:
Originally Posted by NonRubicon View Post
From what I understand the 4.0 doesn't have an EGR valve.

High NOx is usually due to high combustion chamber temps as the final cause. The thing is to find out why you are getting high combustion temps.
What are some of the things that would cause high combustion temps??? I can do the basics like changing oil, brakes, etc...but my knowledge is pretty limited when it comes to this kind of thing
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Unread 04-04-2013, 09:20 PM   #7
Xpress
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Definitely too high of a combustion temperature. What temperature is your thermostat? Have you ran any intake or cleaners through the engine lately? Excessive carbon buildup inside can raise combustion temperatures from an increase in compression. Maybe a clogged PCV system (do they have PCV or CCV systems?).

Quote:
Originally Posted by Prubear View Post
I thought that there wasn't an EGR valve on this year? It's just a hose isn't it?
Quote:
Originally Posted by NonRubicon View Post
From what I understand the 4.0 doesn't have an EGR valve.
Good to know.
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-1996 Jeep Grand Cherokar 5.2L, donor and rainy day driver
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"A well regulated Militia, being necessary to the security of a free State, the [B][I]RIGHT[/I][/B] of the people to keep and bear Arms, [B][I]SHALL NOT BE INFRINGED[/I][/B]."
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Unread 04-04-2013, 09:26 PM   #8
jamesbland123
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Quote:
Originally Posted by Prubear View Post
I thought that there wasn't an EGR valve on this year? It's just a hose isn't it?
There is not an EGR but there is a CCV that basically does something similar, which is adds dirty air into the combustion chamber to reduce the heat produced. The CCV system is on the valve cover, the front and back elbows/air holes. Air is pushed/sucked in the front hose and sucked out the back hose into the intake.

Check this system and look for cracks, etc... The front is an elbow while the back is a elbow with a restrictor orifice, no actual valve. But if this has been messed up for a while you may have to replace your CAT as well. If you don't know much about this system it would be best for you to just pay a smog certified repair to just take care of it. It can get rather expensive to play swaptronics and testing fees to troubleshoot.
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Unread 04-04-2013, 09:31 PM   #9
Reno72
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I just passed my CA smog after failing for high Nox, but I did so much it's hard to pinpoint. I changed all my sensors including MAP and idle, i did a complete tune-up, i replaced and cleaned out all my vacuum sensors (one was clogged), I did an oil change, I ran a fuel system cleaner and I ran a full tank of "guaranteed to pass" before the test. The tech told me many jeeps with bigger tires have a hard time because of the RPM and MPH limits they put on the test, at 15mph & 25 mph many jeeps which have not changed their gears to match the new tires fail. He tested mine in 3rd gear (which he's not suppossed to do) to get a good reading. He suggested having a pair of stock size tires (they can be old and bald) to throw on the rear for the test. I'm choosing to register my Jeep in Imperial county where we have a desert house becuase they don't require smog tests.
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Unread 04-04-2013, 09:48 PM   #10
jamesbland123
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Quote:
Originally Posted by Reno72 View Post
I just passed my CA smog after failing for high Nox, but I did so much it's hard to pinpoint. I changed all my sensors including MAP and idle, i did a complete tune-up, i replaced and cleaned out all my vacuum sensors (one was clogged), I did an oil change, I ran a fuel system cleaner and I ran a full tank of "guaranteed to pass" before the test. The tech told me many jeeps with bigger tires have a hard time because of the RPM and MPH limits they put on the test, at 15mph & 25 mph many jeeps which have not changed their gears to match the new tires fail. He tested mine in 3rd gear (which he's not suppossed to do) to get a good reading. He suggested having a pair of stock size tires (they can be old and bald) to throw on the rear for the test. I'm choosing to register my Jeep in Imperial county where we have a desert house becuase they don't require smog tests.
I've heard of the smaller tires but I'm not sure I completely understand it in relation to NOX. For the NOX test you are allowed a higher value at higher speeds. So at 25 with bigger tires and high gearing (lower number) it would be at an RPM equivalent of running 15 mph which should have a lower NOX. For the other tests that makes sense since the allowed limits are reversed.

Interesting, I didn't know there were places in California that didn't require smog. I have another house in the desert, but unfortunately it's in Kern county which does have smog checks.
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Unread 04-04-2013, 09:51 PM   #11
rshbutch
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Check to see if you have any exhaust leaks,they will give high nox readind
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Unread 04-05-2013, 12:39 PM   #12
Prubear
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my thermostat reads at the normal range...I dont remember exactly what that is but its read the same (right in the middle of the gauge) ever since i bought the jeep. 2 years ago when i failed i just had the whole exhaust replaced and passed with no problem. I was thinking about doing the same this time but only replacing the CAT. I've read that Magnaflow has some pretty good ones. does anyone know specifically what the best one would be. I dont want to spend too much, my wife is already nagging me because i failed the test.
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Unread 04-05-2013, 01:51 PM   #13
rshbutch
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I also live in california,failed smog with high nox. Was told to check for leaks,had several exhaust manifold bolts loose as well as my down pipe.
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