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Failed CA emissions w/ high NOx....and yes, I searched

SanDiegoXJ

SanDiegoXJ

NAXJA Forum User
Location
San Diego, CA
Ok, so I took the Jeep in today for a smog test pretty confident it would pass. It failed with the following reading:

15mph 1713rpm CO2 14.8% HC 13/89 CO .02/.66 NO 1138/517
25mph 1661rpm CO2 14.8% HC 9/54 CO .02/.80 NO 877/770

I have '94 4.0 with a Borla Header and Borla catback (both 50 states legal).

The exhaust was just put on a year ago along with a new Cat.

I'm guessing, given the readings of the HC and CO that the cat is fine.

I'm planning on getting an 02 sensor, but anything else that could raise the NOx that high? I over doubled the limit at 15 mph. Would just taking the car in cold help? All other readings not only passed but were below average.
 
SanDiegoXJ said:
Ok, so I took the Jeep in today for a smog test pretty confident it would pass. It failed with the following reading:

15mph 1713rpm CO2 14.8% HC 13/89 CO .02/.66 NO 1138/517
25mph 1661rpm CO2 14.8% HC 9/54 CO .02/.80 NO 877/770


I just failed mine on NOX too. I also doubled the limit on both 15mph and 25mph

15mph NO 2200/1015
25mph NO 2140/875 the 2nd # being MAX. Everything else was perfect, I could even pass CO and HC in san diego. I'm going with a cat.
Mines a 92 4.0 borla header, generic cat and a spin tech muffler.
By the way look on your emissions lable under the hood. My original NO limit says 1.2. I believe that means 1200.
What does yours say?
Click to expand...
 
JXPEEJ said:
I just failed mine on NOX too. I also doubled the limit on both 15mph and 25mph

15mph NO 2200/1015
25mph NO 2140/875 the 2nd # being MAX. Everything else was perfect, I could even pass CO and HC in san diego. I'm going with a cat.
Mines a 92 4.0 borla header, generic cat and a spin tech muffler.
By the way look on your emissions lable under the hood. My original NO limit says 1.2. I believe that means 1200.
What does yours say?
Click to expand...

Don't see an emissions label. But I'm hesitant to replace the cat since it's so damn new.

I should probably mention that I also just added new fuel injectors (Mustang 5.0 injectors), a new fuel filter. I thought about changing the plugs, but I was under the impression that new plugs would make it run hotter, so I was hesitant to do that. Currently it's just running Champion truck plugs.

Also, I just checked all the bolts on the intake/header. They appeared to be a little under torque, so may have a been a leak there.
 
I have to replace my cat EVERY time I smog. This time I just went straight to the test only, without pretesting and got nailed. I think that a new cat is only good enough to pass on the same day you put it on. I think one might want to install a new cat, drive to the smog test....pass the test...
and then trailer the jeep home and never drive it till your next smog is due....Repeat every two years and your cat will live a full life.
 
JXPEEJ said:
I have to replace my cat EVERY time I smog. This time I just went straight to the test only, without pretesting and got nailed. I think that a new cat is only good enough to pass on the same day you put it on. I think one might want to install a new cat, drive to the smog test....pass the test...
and then trailer the jeep home and never drive it till your next smog is due....Repeat every two years and your cat will live a full life.
Click to expand...

Well, you bring up a good idea....buy one for testing only....they're not that tough to swap =)
 
cat shouldn't really make that much difference in nox, it might bring everything down just enough to eek through, but it probably isn't the main issue. high nox is caused by the combustion chamber temp being too high, mainly either because of a lean a/f ratio or a lot of carbon build up in the chambers. if you're sure it's not running lean for some reason then try seafoaming the hell out of it, or the mopar combustion chamber cleaner.
 
Did seafoam not too long ago. I've been out tightening the bolts on the header/intake. 1 is missing at the number 1 cylinder. All but one of the others were loose....at least half a turn, if not a full turn, loose. I'm hoping that was allowing enough air into the chamber after the map sensor to cause the high NOx. All I know is it passed before, now I've changed the exhaust, replaced the cat, replaced the injectors, replaced the plugs/wires, and replaced the cap/rotor since, and it got worse. :dunno:

Guess I'll do the redneck vacuum leak test with a can of carb cleaner and see if that yeilds any results.

I will say though, regardless of test results, she purrs like a kitten....perhaps a kitten in heat, but still... =)
 
Just an update...

I replaced the missing bolt and torqued the header/intake back down to spec in the hopes of resolving the high NO readings that generated my initial failure....the NO reading got worse =( I guess I was losing 200ppm in the exhaust leak, because that's what it went up on both readings....on a good note, the HC went down even further. =)

So the guy at the smog shop (different guy/same shop) says the most obvious thing is the converter. He says mine is too small and that I should get a Walker cat from NAPA. He says there was a recall on the OEM one because the NO levels were so high and they now require a larger heavy duty cat to aid in the NO reduction...(I'm starting to remember reading something about 2 way vs. 3 way cats).

Does that sound legit? As I recall, I thought my old one was much larger than the new one, but I just chalked it up to new technology.
 
I don't know about the recall but it's possible. They got this stuff good enough to run without an EGR valve so I would not be willing to blame poor factory spec.

Three-way means that there are three conversions. First the nitrogen oxide is split to produce plain oxygen and nitrogen, then the oxygen is used to reduce the hydrocarbons and convert the carbon monoxide to carbon dioxide. If the HC and CO levels are fine then the cat is probably working okay.

High NOX results from high exhaust temperature. You are most likely running lean, which is why the first action is to replace the O2 sensor. Another possible problem is with engine deposits that are burning off. It may be the cat but I would try the easy and cheap fixes first.
 
ehall said:
You are most likely running lean, which is why the first action is to replace the O2 sensor. Another possible problem is with engine deposits that are burning off. It may be the cat but I would try the easy and cheap fixes first.
Click to expand...

Yeah, I was hoping the loose intake was the lean error....apparently, I was mistaken. =)

As for the the cheaper alternatives, the cat I bought was $86 and the 02 is $68....so it's pretty much a toss up as far as funds are concerned. My most recent concern is that since I got a $86 cat, perhaps I only got the 2 way and not the 3 way, which would again suggest a viable reason for high NO. Either way, end result is it's not getting fixed until the next paycheck shows up and credit card bills are paid at the first of the month...at which point I'll probably just buy both the 02 and the new Cat and cross my fingers.
 
I just got back from Test only with mine and have High CO2, small mis-fire. It has new plugs, rotors and wires, can't find a vacuum leak any thoughts?

Thanks,
Tom
 
So think I just found my problem. =(

I looked up my catalytic converter from the place I purchased it from and it said Fits: All (Others said Fits: 49 States)

As I did some research on the part number provided, I find the following:

Direct Fit Catalytic Converter Unit, Not For Use On California Emissioned Vehicles. Auto Parts Warehouse has extensive Catco Catalytic Converter catalogs.We are now offering FREE shipping on all Catco Catalytic Converter orders over $50.00. Our secure catco catalytic converter catalog is available every hour of everyday. Shop with confidence for all your catco catalytic converter needs. Catco Catalytic Converters are In Stock and available today. Save upto 60% off dealer price on your next Catco Catalytic Converter purchase. Our online catalog contains a wide selection of the OEM and aftermarket parts you need at unbeatable prices

Too bad that wasn't mentioned on the site I purchased it from. =(

Guess you get what you pay for.
 
Last edited:
Boatwrench said:
I just got back from Test only with mine and have High CO2, small mis-fire. It has new plugs, rotors and wires, can't find a vacuum leak any thoughts?

Thanks,
Tom
Click to expand...

Well, my first guess would be carbon build up in the combustion chamber. Seafoam would take care of that I think. However, I've heard of Seafoam clogging cats and screwing up o2 sensors, so I generally use it only when I plan on changing both. Then I'll run a seafoam treatment before changing them out so the old parts collect all the crap and the new parts stay all pretty and clean...for instance, when I get my next paycheck I'll run seafoam through it, pop in a new sensor, and buy a cat locally so it actually meets state standards. =(
 
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