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Unread 04-25-2013, 02:55 PM   #1
micellis
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1998 ZJ 
 
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Failed NOx Emissions

Just moved to Colorado and went to get emissions done. CO, HC both passed, but the limit for NOx for CO is 2.5 GPM and I ran at 3.9 GPMs. I am a bit shy of 220k miles so I am wondering what all I can do to get this baby fixed up. Had a full tuneup done less than 15k ago with Plus, wires, Distributor cap and rotor. Oil is about 2500 miles old. Any other ideas? I changed the TPS out about 4k ago. Anything else I could be forgetting that might help?

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Unread 04-25-2013, 05:27 PM   #2
ratmonkey
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always go in on a fresh oil change. bet that will clear up your nox actually.
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Unread 04-25-2013, 08:55 PM   #3
micellis
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That was my thought, I am going to change it this weekend and I have 10 days to get a free reinspection done. I was considering a seafoam as well
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Unread 04-25-2013, 09:28 PM   #4
95grandc
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It could be your cat. But did you move to Denver, CO? Because in CO, there is no emissions.
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Unread 04-25-2013, 10:01 PM   #5
micellis
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Quote:
Originally Posted by 95grandc View Post
It could be your cat. But did you move to Denver, CO? Because in CO, there is no emissions.
Yeah I'm in western Denver
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Unread 04-27-2013, 01:07 PM   #6
tetatdo
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usually its the cat. make sure you get a 3 way put on. Magnaflow has a specific model that fits the GC
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Unread 04-27-2013, 01:35 PM   #7
jnicewan
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A few of things that can cause high NOx are not adjustable on the 4.0L (fuel mixture, timing, ) Often high NOx is a result of high combustion temperatures and the key emissions components that reduce NOx are EGR and Catalytic Converters, pretty sure you dont have an EGR. If available try finding 100% gas and low octane. Carbon deposits in the combustion chamber can lead to higher NOx levels so you might try a combustion cleaner like Sea Foam. A lean running engine causes high combustion temps too so clogged injectors, vacuum leaks etc need to be eliminated. Higher engine temps, make sure its not running too hot.

I dont know what kind of driving you primarily do but a good highway trip can help clean things out too, either that or drive the snot out of it for a little while. Also do a good highway cruise before you take it back for inspection, along with fresh oil and gas.
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Unread 04-27-2013, 02:32 PM   #8
jetjr91
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Same thing happened with my 93 4.0

Everything passes and barely registered except the NO.
I did the same thing changed oil and spark plugs helped but still high on the NO.
The problem on mine was the o2 sensor. It wasnt dead but it wasn't working right either. We call it a lazy o2 sensor, doesn't send the right info. Maybe try that out. After changing the o2 the NO barely registered.
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Unread 04-30-2013, 04:26 PM   #9
micellis
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Yeah, did an oil change and a seafoam, also changed the air filter and cleaned the box out. Did a little better on the NOx but still failed. Was previous at 3.9 GPMs of NOx, the woek I did dropped it to a 3.5 GPM. My next step is to decide whether to change the O2 sensors and clean MAF, or just go for a new Cat. I'm pretty sure it's a stock Cat, any recommendations?
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Unread 04-30-2013, 05:36 PM   #10
jetjr91
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Quote:
Originally Posted by micellis
Yeah, did an oil change and a seafoam, also changed the air filter and cleaned the box out. Did a little better on the NOx but still failed. Was previous at 3.9 GPMs of NOx, the woek I did dropped it to a 3.5 GPM. My next step is to decide whether to change the O2 sensors and clean MAF, or just go for a new Cat. I'm pretty sure it's a stock Cat, any recommendations?
On my 95 v8 it passed smog 4 months ago with the factory cat and its rattling inside.
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Unread 04-30-2013, 06:52 PM   #11
95grandc
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What year is your jeep?
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Unread 04-30-2013, 07:33 PM   #12
micellis
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Its a 98 4.0 Laredo. debating on just changing both O2s and the cat and being done with it.
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Unread 04-30-2013, 08:32 PM   #13
Virmagicus
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It's the cat... i'd bet my left one.
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Unread 04-30-2013, 11:17 PM   #14
jnicewan
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Quote:
Originally Posted by micellis View Post
Its a 98 4.0 Laredo. debating on just changing both O2s and the cat and being done with it.
If your low on funds and decide to change the O2 sensors, just change the front one. The front O2 influences fuel mixtures, a failing sensor could cause either a lean/rich condition or both, the rear O2 is just a catalyst monitor, basically it only monitors the efficiency of the cat.
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