Emissions NOx failure

Hi all.

I paid a visit to the AZ Dept of Environmental Quality and Failed my Emissions Check.

The 90 XJ 4.0 passed emissons in Tucson 4 months ago, and Maricopa county checks NOx which failed me.

Readings from 05/08: (loaded/idle)
HC - 77 - 220 pass , 81 - 220 pass (Parts per Million)
CO .69 - 1.20 pass , 1.09 - 1.20 pass (%)
gas cap pass, cat conv pass, air system n/a

Readings from 08/08:
HC - 1.56 - 2.00 pass (grams per mile)
CO - 15.83 - 20.00 pass (grams per mile)
Nox -9.96 - 4.00 FAIL (grams per mile)
gas cap - fail (I did change to a Stant locking cap in July), pressure test - pass, evap componants - pass

At any rate. I have since changed fuel filter (was leaking) and ran a bottle of fuel injector cleaner with a tank of gas. I took it to a shop to check for any cooling issues that might create the NOx problem it has been running 210+ when I tortured it climbing hills in 110 degree weather. They recomended an Aluminum radiator, but nothing as far emissions. I had just replaced fan clutch, Idler pulley, and Renix coolent bottle.

So any ideas?? Specifically what cranks up NOx but keeps everything else inline? Egr? O2? I haven't tried the Seafoam treatment. The engine is a rebuild with maybe 15k miles on it.

Thanks.

BTW Tires are 31" if that matters for the big rollers they had it on.

nox issues, especially in a renix, are primarily a result of egr valve issues. check the egr out. you'll probably find that it's not opening, or that it's passages are clogged solid with carbon-y crap.

the cat convertor has lost its efficiency

jneary said:

the cat convertor has lost its efficiency

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how do you test the cat?

mrpeepers said:

how do you test the cat?

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Knock out the insides?

Sorry Alabama has no emmisions testing and I just say take it all off. No EGR then no need for a CAT.......right? All you really need to do is monitor you AFR and keep it cool. But I suppose for emissions you have to have both of those things.

my jeep failed due to this reason as well, I replaced the cracked header and a blocked up airfilter and plan on going back to retest today. *the airfilter was so blocked the jeep had sucked it up into the intake tube, I gained 5mpg just changing the filter alone*

Get the EGR valve replaced and the EGR tubes cleaned out

check also, for ANY vacuum leaks as lean mixture (too much air) will exponentially increase combustion temps and promote formation of NOx.

Back some years ago my 89 4.0 MJ failed for high NOx. The cat was rattling, and I though that might do it, but a neighbor of mine who's an expert at Snap-on 7 gas analysis (sniffer stuff, basically, what comes out tells you what's wrong with the motor) said that my 4.0 barely needed a cat, and that I should do the EGR valve.

I did, left the rattling cat alone, and it passed with the rattling cat!! This was probably in like 00 or 01, and at that time the EGR valve (need the seal too) was a dealer only item, and IIRC it cost about 90 for the EGR valve and 5 for the gasket. I'm sure by now they cost about 500 bux!!

I noticed lower engine temps and better performance once I changed the EGR, in addition to the added bonus of passing MA state emissions!

when mine didnt pass last year for nox (94) I changed the o2 sensor...worked like a charm.