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Old 11-30-2013, 01:15 PM   #1
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Emissions FAIL Twice High NO

Took the Ohio E-Check test today, failed. High NO levels limit:1163 Reading:1708.4
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Then I went to autozone and asked for their advice (bad idea) the told me to put in some "dry gas" to remove the moisture from the tank. Took the test again and...FAIL Reading:1902.4 HC rose and CO decreased.
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I don't know what's causing this. Could it be my bad PCV valve? My oil too high? Just replaced my oil pressure sensor. Check engine light is NOT on. '95 with a 4cyl, any ideas??

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Old 11-30-2013, 01:18 PM   #2
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How old is your cat? Since we don't have EGR valves ( I too have a '95 2.5L) the cats will fail sooner then vehicles with EGRs. Also have you done anything to lean your engine out? Bad CATs will raise the NOx level and bad O2 sensors will also cause high NOx levels. You may not always get a CEL with a faulty O2 sensor. Pull the "key trick" and see if you get code # 21, 51, or 52.

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Old 11-30-2013, 05:15 PM   #3
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What year, and engine?

Basic rule of thumb for NOx:
Exhaust leaks before the cat converter
Os sensor (rich reading that might be false tells the computer to run lean).
Vacuum leaks

Anything that can cause the engine to run HOT or LEAN.

The 4.2L Jeeps re famous for leaking Pulse AIR injection systems, flooding the cat with air, disabling the NOx reduction.
The 4.2 is also famous for Vacuum lines breaking, leaking and this can cause the EGR to not function, that EGR is IMPORTANT to lowering NOx in the 4.2L

Ths 2.5LTBIs main issues are bad O2 sensors, and low fuel pressure causing a LEAN condition

The 4.0L and PFI 2.5L main issues are low fuel pressure, bad O2 sensors, and carbon on the pistons, raising compression causing higher burn temps.

ALL YJs have BAD issues with cracking exhaust manifolds, any exhaust leak before the cat renders the NOx reduction portion of the cat converter useless.
Also PCV systems plug up and raise CO, but if the line cracks and leaks there is a lean issue and Chrisler has an upgrade kit to help reduce this from happenign in the future (you might not even be able to get the normal parts, only the kit).

However, to get into more detail, we NEED your Year and Engine information.
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Old 11-30-2013, 07:39 PM   #4
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He said it was a 95 2.5L
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Old 11-30-2013, 08:54 PM   #5
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Quote:
Originally Posted by CyndiB View Post
He said it was a 95 2.5L
BAH! thats what I get for looking at the pics, an not finishing the post!

YJzehe, Check for ANY exhaust leak before the Cat Converter, and if there are none, have a "Well Known" exhaust shop check your Cat, ideal CO2 should be 14.7%, you are a bit below that.
Most exhaust shops will check your cat for free, but try to find one with a good reputation, they will be less likely to just sell you a cat without checking it first.
Also, have them check the O2, its a pretty simple test, done with a digital oscilloscope, and a common procedure, if your O2 is misreporting a richer mixture, your computer leans out pulling fuel, not normally seen with your CO2 and CO readings, but it can have an affect.
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Old 12-03-2013, 02:34 PM   #6
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I just took the test again today, after having replaced the oxygen sensor and pcv valve grommet, which has been leaking for awhile. I checked all vacume lines for cracks and replaced one the rest were good except one that was disconnected, fixed that one too. Still another fail, NO was even higher 1935. I think I'm just going to buy a new cat. In Ohio the first 3 fails are free of charge after that they cost $18. There are some exemptions, if I show a 30% change for the better and have spent more than $200, I can be waived. If I've spent $300 with no improvement I can also be waived.
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Old 12-03-2013, 02:38 PM   #7
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I think you need a new cat...can you weld or know someone who can?

It'll save a ton of money if you do!

Here's the cat ---->http://www.wermopar.com/oem-part/jee...erter/52020110

Again, I highly recommend you do it yourself because an exhaust shop will want over a grand to do it, then they'll sell the old cat and make more money off of you.
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Old 12-03-2013, 05:42 PM   #8
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Originally Posted by StangWrangler View Post
Again, I highly recommend you do it yourself because an exhaust shop will want over a grand to do it, then they'll sell the old cat and make more money off of you.
If any exhaust shop is charging you that much, they are going to go out of business, Im in Cali, and Cats for YJs are around $250 installed ($350 if you are a stranger).

Its also illegal to resell a used cat here, but thats just Cali...
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Old 12-03-2013, 08:26 PM   #9
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I got a new cat and Magnaflow muffler for around $350
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Old 12-03-2013, 08:52 PM   #10
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I have nothing to help here but seeing posts like this make me very happy to live in the dirty south where we don't have ANY inspections like this. Good luck.
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Old 12-12-2013, 08:11 PM   #11
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fourth test was taken today. Another fail after changing my cat, muffler and tail pipe. NO still the reason for failure 1,500 ppm. So far I've changed vacuum lines, ccv valve gromet, oxygen sensor, cat & muffler. I've checked the header and down pipe for cracks there was nothing. WHAT IS GOING ON!?
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Old 12-12-2013, 08:42 PM   #12
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Have you checked for manifold leaks? These Jeeps are notorious for cracked/warped manifolds and that'll cause high NOx.

Usually someone would have piped in by now and mentioned the old sea foam and higher octane fuel trick. I recently replaced my motor so I had them run the pretest before doing the actual test. It came in 6 ppm below max, yikes! Brand new engine so Sea Foam wasn't needed but I did put some 89 octane in before the actual test and it lowered the NOx by almost 200ppm. Mines a 87 4.2L so you may get a different result.
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Old 12-13-2013, 01:15 AM   #13
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Go to WalMart and buy a fuel additive called "Guaranteed to Pass". I have used it twice on vehicles that failed miserably and it worked both times. Your local auto parts store should sell it, too.
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Old 12-13-2013, 12:05 PM   #14
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My 92' 4.0 was high on the Nox reading, mostly due to a leaking exhaust manifold. Lean conditions caused in part by vacuum leaks will lead to high combustion chamber temps and in turn higher Nox readings. It's a snowball effect that can take out o2 sensors and cats , I would strongly suggest you seek out vaccum leaks first then work your way back, guaranteed to pass did not work for me.
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Old 12-13-2013, 02:36 PM   #15
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So today I changed my spark plugs, because bad plugs can cause unburnt gas to be present in the exhaust? Also tried running a 1/2 can of SeaFoam through the vacuum line on the break booster, let it sit for 15 mins, started and nothing happened, no smoke no loss or gain of power. Didn't take the test today, I am still looking for what the issue could be. If all else fails I have to buy something that seems like it could help and costs more than $80 any ideas?

Quote:
Have you checked for manifold leaks? These Jeeps are notorious for cracked/warped manifolds and that'll cause high NOx.
Quote:
My 92' 4.0 was high on the Nox reading, mostly due to a leaking exhaust manifold. Lean conditions caused in part by vacuum leaks
I have checked the manifold and the vacuum lines
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Old 12-13-2013, 05:09 PM   #16
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Go back and read 2xs' first post, he s a smog tech. I think you've replaced everything he suggests except he keeps repeating low fuel pressure being a cause for high NO. I don't know how to fix low fuel pressure, but maybe that might be your next direction. I used Seafoam in my gas, maybe that would help since you already have a can. It's supposed to help clean the fuel lines and injectors. Good luck, don't give up!
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Old 12-13-2013, 06:36 PM   #17
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I'm curious where in Ohio you still have E check ?
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Old 12-13-2013, 06:41 PM   #18
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OK I just looked it up. There are only 6 counties in Ohio that still have E-Check. I thought we got rid of them state wide.
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Old 01-08-2014, 07:53 PM   #19
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I am in southern CA and my 93 yj wont pass smog either. I replaced my cat plugs o2 sensor and ran seafoam in it. I am only failing nox, it needs to be at 513 but the lowest I got it too was 630....so close. This is the first I am hearing about a leak in the manifold before the o2 or cat causing high nox levels. I did notice while I was using the seafoam there was white smoke coming from my manifold I guess that is my next option. and yes I know moving is one but I cant move I have a career here that I cant leave.....in any other state my yj would pass flying colors
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Old 01-08-2014, 09:42 PM   #20
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I had a similar issue with my jeep last spring. I replaced the cat, ia sensor, o2, tuned it up, seafoamed it verified no exhaust leaks I was still failing smog on NOx.

I talked with an old timer from the racetrack. He said high NOx is due to high temp in cylinder and said run high octain race fuel in it and take it in for the smog. I was at my last hope on getting a pass. I passes with such low numbers the smog shop thought I did a motor swap. Five failed attempts and finally a pass. It worked for me but I will not guarantee anything. Best of luck.

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