Need help! Just bought a yj and failed emissions.wife is going to kill me hahahaha - Jeep Wrangler Forum

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Old 10-22-2016, 12:39 AM   #1
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Need help! Just bought a yj and failed emissions.wife is going to kill me hahahaha

I have high NOX and slightly higher hc. I'm told it's either the CAT or EGR. I haven't looked but i dont think 1994 wranglers have a egr valves...!?!?Idk?!?!? Please help I am new to jeeps and this forum.
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Old 10-22-2016, 03:43 PM   #2
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Its nearly always the cat with the high NOx. The 94 uses a THREE WAY cat. (HC/CO/NOx)
That's what you need to get. They are more expensive, but the cheaper two way cat wont fix your NOx.

You would be wise to change out your O2 sensor, and tune up parts(plugs, cap, rotor, wires, filters) before trying again.

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Old 10-23-2016, 01:52 PM   #3
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Indiana has emissions?? I'm in Illinois and we don't have them here i don't even have a cat on my jeep. And yeah YJ's don't have EGR, might wanna seafoam it too it helped a friend of mine in cali pass emissions on a old 2.8 Chevy blazer.
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Old 11-03-2016, 08:56 AM   #4
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You own a YJ.. You need to get used to your wife being mad. As soon as you get this fixed there will be something else to fix.
Last year I had mine inspected it had high NOx. I replaced the cat and it passed.
Mine passed 24 Years old so no more Emission tests. Safety check only
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Old 11-07-2016, 04:52 PM   #5
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We used to use a lot of bottles of dry gas to drop the emissions. Not sure if it would work in your case or not.
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Old 01-16-2017, 09:14 PM   #6
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It will most probably be the Cat, it could likely still be the original and has deteriorated internally.
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Old 01-18-2017, 10:24 PM   #7
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It's probably the cat.

However, your Jeep uses a forced orifice instead of an EGR Valve. There is usually a plate below the orifice. The plate would be inside the valve cover. Cheap oil and/or poor maintenance can lead to lots of crud developing on the plate. The crud can block the orifice. This is usually an extreme problem.
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Old 01-19-2017, 08:50 AM   #8
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I'll give you $1,500 for it..... hahaha I live in Michigan, thank goodness for no emission tests!!!!
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Old 02-24-2017, 11:17 AM   #9
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My Y J is registers in California. The guy that does my smog loves it he says the ones with E.F.I. pass with no problem. and he don't like to do the one's with carburetor's because they wont pass and the owners get pissed and blame him because they wont pass.
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Old 03-01-2017, 01:03 AM   #10
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Every time I see people say "Oh yea, high NOx is a cat" I cringe.

NOx is created by HEAT when the cylinder fires.
NOx is reduced by the front half of the cat. If the front half of the cat is being fed too much O2 (flooded), it will not work.
ANY exhaust leaks before the cat will cause this (Main problem with our Jeeps).
A Biased rich O2 will fool the computer into running leaner causing too much NOx (#2 issue with ourr Jeeps).
A LEAN mixture will create extra heat and NOx in the process.
Spark plugs with the wrong heat range will cause high NOx.
Ever replaced a freeze plug, couldnt get the old one out so pushed it into the block (or thet lazy mechanic at your local speedy tune)? You just created a hot spot in the cooling system, and up goes your NOx...
Gear ratio change? (I went from 3:07 to 4:10 and caused a BIG NOx issue with my '94 4.0L AX15) you could easily put your jeeps load vs speed into a NOx heavy powerband on the smog dyno...
Excessive carbon on the pistons and combustion chambers will raise compression, the carbon will hold heat and cause pre-ignition and the result is... High Nox.

And LAST, a damage cat will also cause high NOx

HC is un burnt fuel, raw gasoline, a misfire to be blunt.
HC is a direct result of fuel not burning, and a tune up is normally in order.
If you do a tune up, PLEASE use stock Champion Copper spark plugs, too many people get "upsold" into double platinum by the parts "professional", just dont fall for it, use the Champion cheap plugs.... Trust me...

I live and work in Cali, we measure our tailpipe gasses by PPM instead of % (except for CO, and CO2), and the translations can be odd, but the gasses are all the same, and gasses that are too high have the same repairs no matter how you measure them.

Quote:
Originally Posted by wcjeep View Post
It's probably the cat.

However, your Jeep uses a forced orifice instead of an EGR Valve. There is usually a plate below the orifice. The plate would be inside the valve cover. Cheap oil and/or poor maintenance can lead to lots of crud developing on the plate. The crud can block the orifice. This is usually an extreme problem.

This is wrong on 2 levels,

No, the injected 4.0 has no EGR.
An EGR will directly reduce NOx (it is its primary function).

However:
Any EGR system will NEVER go to the valve cover... One end goes into the intake manifold, to full vacuum, the other goes to the exhaust, with a ported vacuum line on top to open it up under load

This orifice you speak of is the PCV, a totally different emissions system...
The PCV system purges gasses that escape through the piston rings during compression, and sucks them out to be re-introduced into the air/fuel mixture...

Quote:
Originally Posted by DREDnot View Post
....snipped out a part to maintain my sanity... The 94 uses a THREE WAY cat. (HC/CO/NOx)
....snipped out another part to maintain even more of my sanity... They are more expensive, but the cheaper two way cat wont fix your NOx.

You would be wise to change out your O2 sensor, and tune up parts(plugs, cap, rotor, wires, filters) before trying again.
Good advise...
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Old 03-04-2017, 09:01 AM   #11
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It would have been better to say Fixed Orifice. The 4.0 does not have a PCV. It's technically a CCV system. Originally designed for military Jeeps to keep water out of the block. The original CCV system had nothing to do with emissions.



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Old 03-04-2017, 11:58 AM   #12
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Quote:
Originally Posted by wcjeep View Post
It would have been better to say Fixed Orifice. The 4.0 does not have a PCV. It's technically a CCV system. Originally designed for military Jeeps to keep water out of the block. The original CCV system had nothing to do with emissions.



The point was, its not an EGR...

Its original design is keeping combustion gasses out of the crankcase, and started life as a road draft tube. Any incarnation of this system is still for that same reason. Keeping water out of the oil is a secondary benefit.
Combustion gasses destroy oil, and bearings. it keeps those EMISSIONS out of the atmosphere by going to a closed system.
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Old 03-04-2017, 12:05 PM   #13
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My 94 4 banger also has a ccv system which does get clugged up.
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Old 03-04-2017, 03:44 PM   #14
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OP has one post, dated 10-21-16.

I wonder if he ever got it fixed and if he still checks in on this forum.

Good Luck, L.M.

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