'88 Failed Emission: High NOX HELP - JeepForum.com
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post #1 of 2 Old 11-25-2011, 02:18 PM Thread Starter
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1988 YJ Wrangler 
Join Date: Jan 2007
Location: arizona
Posts: 426
'88 Failed Emission: High NOX HELP

Hey everyone...I have a 1988 YJ, 4.2, nuttered, Motorcraft 2100, Team Rush upgrade and it failed Az emissions with high NOX. The readings are as follows:

My Vehicle / Applicable Standards

HC 2.01 / 3.00 Pass
CO 5.84 / 25.00 Pass
NOX 9.59 / 4.50 Fail

Any ideas what I should do to make that NOX pass? Please help.

The little booklet they gave me has a few things listed that may cause that problem:

* Removed, plugged or malfunctioning EGR system (mine is still on)
* EGR valve
* EGR exhaust gas ports, lines and passages (what is that?)
* Abnormal engine operating temperature (mine doesn't overheat or anything like that)
* Air management system malfunction (what is that?)
* Lean air/fuel mixture (mine runs great....except when it warms up, it idles at around 600 rpms...pretty low I think)
* Catalytic converter efficiency (what's that mean?)
* Over-advanced off-idle timing (I don't know where mine is set at, but it runs really good)

It also failed the pressure test, but I think I know what the problem is there. When I filled up with gas the other day, I had some gas "overflowed" on the top of my gas tank. I think it's the rubber grommets on the vent lines to the rollover thing. I ordered those grommets online, but I'm going to see if I can find some at checker auto or autozone.

I have about 2 1/2 weeks left on my temp tag, so I need to get this through emissions sooner than later.

Thanks in advance...


Last edited by SamzJeep; 11-25-2011 at 02:19 PM. Reason: mistake
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post #2 of 2 Old 11-25-2011, 02:42 PM
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1995 YJ Wrangler 
Join Date: Feb 2009
Location: Los Angeles. California. United States.
Posts: 4,910
Vacuum lines
Cat converter

Thermostat keeps the Temp optimal, too cool equals not good emissions.
Incorrect, bad, or wrong vac lines, equals emisduons problems.
Bad or clogged cat converter means fail for emissions too as it is a filter of its own purpose.

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