Well, failed my emissions test yesterday, the reading that failed was a high NO output. What causes higher NO output? and will a new catalytic converter cure this?

I can just get $300 worth of work done, and they'll give me a waiver for two years, but I don't want to be in this same boat two years from now.

I do plan on getting haveing my engine rebuilt in two years, so shelling out some dough for a new header, cat, and a cat-back system would not be that bad of an idea, and then get the two year waiver.... But I'd like to know what causes a high NO output.

Any emission gearheads out there?

what engine.. ???
carbed of f.I.???

is the manifold cracked??
is there any exhaust leaks?
is the o2 sensor new?
there is alot of things that could make it that way..
new computer if there is one..lol
dist not advancing right..
is the egr valve working right?
any vacum leaks?
not enough info to tell you ..lol

Originally posted by mikesimpson
.... But I'd like to know what causes a high NO output.


EGR valve problems would be the first place to look. The EGR valve is specifically for NO problems.

A new catalytic converter is not likely to cover up any NO problems. Cats are for CO and HC. Some newer cats will take care of NO, but if it was a cat problem, I would suspect the other gases to be affected.

Clean the throttle body GOOD! new plugs, wires, cap, rotor. Drive the Jeep hard(on the freeway) for about 15 mins before taking it in to the shop and make sure they check it while the cat's still hot. As they said, exhaust leaks, o2 sensor?, vacuum leak?, etc, etc.

FYI: sig says '91 YJ so likely EFI 4.0L

Looks like I'll pick up a new EGR, plug wires, rotor, cap etc, and give the throttle body a good cleaning. I know the cap, wires and plugs need changing.

The exhaust is beat, but I'm thinking there is something wrong with the burn / combustion to create a higher than normal NO output. And since the cat converter, scrubs for CO and HC, and not NO, then I'll go with the combustion and EGR avenue.

Thanks all for your input, it is greatly appreciated. ;)

If anyone's got anything else then chime in. And yes, it's a 4.0ltr, fuel injection motor. Haven't screwed with anything along the 'puter avenue.

And what the heck, may as well pick up an O2 censor as well.

OK, here's an update, the 4.0ltr does not have an EGR valve.....

Would the PCV make a like change to the combustion??

Color me ignorant, but how would a leak in the exhaust system cause high NO output? I'm not being a smart ass, just wondering...

From what I'm thinking a higher NO output would be the result of improper combustion properties, not with what goes past the exhaust valves and through the exhaust.

An exhaust leak CAN change the reading the O2 sensors gets, and cause a corresponding leaning out of the mixture, which would cause high NOX.

Originally posted by withamc
An exhaust leak CAN change the reading the O2 sensors gets, and cause a corresponding leaning out of the mixture, which would cause high NOX.

Yup! exhaust leak will mess everything up. O2 sensor will read more oxygen, will adjust with more "fuel"?, high NOX. I was failing a few months ago. Ended up getting new cat, O2 sensor, and cleaning blowby out of throttle and tubes to "patch" the prob. I passed but it still had high numbers. All because I still have a small exhaust leak at the header. Well, that and/or vacuum leaks at the intake manifold/vac lines.

I have a crack in my exhaust manifold ..
I have to change the cat out a few extra times..
and replace the o2 sensor.. before the next smog..
the o2 cant help but realy lean out the system till it runs red hot..
and the exhaust is burning out..

i don't know about the inspection procedures in your state, but i have a MA sticker license, and when we have a car that we want to pass but has high nox readings, we test the car under what's called a 2 speed idle, instead of on the dyno. technically it's only supposed to be used on vehicles with awd or traction control etc that can't be tested on a 2wd dyno, but if you can convince the inspector to do it, it puts no load on the engine like the dyno test does, and produces much lower nox readings.

I always get worried when a person posts a method for circumventing laws online... but this is also this guys very first post... just bothers me ya know???:confused: :confused:

Originally posted by fatconnors
i don't know about the inspection procedures in your state, but i have a MA sticker license, and when we have a car that we want to pass but has high nox readings, we test the car under what's called a 2 speed idle, instead of on the dyno. technically it's only supposed to be used on vehicles with awd or traction control etc that can't be tested on a 2wd dyno, but if you can convince the inspector to do it, it puts no load on the engine like the dyno test does, and produces much lower nox readings.

If you have the stock tires they might help and I use a bottle of rubbing alcohol to get mine to pass. I got the 258 with the MC2150 on it. Change the oil and make sure the air filter is clean. Are you sure the waver is for 2 years I thought it was for just 1 year if you put $300 into the repair.

sorry to worry you apeters, but the guy was looking for options. you might want to pay 300 dollars to pass emissions, but for some people "circumventing" the law is a better choice. he doesn't have to do it, neither do you. but my rig isn't exactly perfectly legal as i'm sure many aren't, and you get a lot less grief from the cops with a valid sticker, however it was obtained.

I didn't see anything wrong with fatconnors post, he seems perfectly qualified. State to state is different, I know living in
"CALIE-FORNIA" and the crap I went through with an OBDII 2002 4.0L in a '88 Wrangler. I wanted to CHEAT the bastards any way I could. Fatconnor, keep the post comming, Terry

Fatconners,
Fuck yeah brotha....Say it like its supposed to be said. I completely agree with you on this one. Luckily, in kansas we dont have to deal with too much of the bs with the theoretical global warming shit that is scientifically proven that the earths heating in cooling is related to sun spots. BLAME IT ON THE SMOG. Not some bullshit idea.
Sorry guys just had to vent. Just my 47.5 cents
Later

Since the inspection is every other year, that would be a two year waiver.

Well, I'm gonna start with new plugs, rotor, cap, wires, TBI cleaner, and some miracle liquid crap from a local auto store, oil change with synthetic, a new O2 sensor, a new PCV valve, and check my air tubes and vaccum tubes for blocakages and go with that.

If it still fails, then I'll get a new header, a 3-way CAT and a new cat back exhaust....

Thanks for all the input;)

Good luck man you got some work ahead of ya. Hope ya pass. and if nut. Just stand in the parkin lot and get the referees attention and :flipoff2:

I have posted this before, but I guess I'll do it again.

I was getting hight NOX on my 4.0L (like 2x the limit). Everything else was way below the limit. I had a relatively new cat (<3 yrs) and new 02 sensor and header. I tried cleaning the combustion chamber and it made no difference. Then, I went out and bought a 3 way cat from Napa and put it on. After that, I passed NOX with flying colors. I'm guessing the exhaust shop put on a 2 way cat which doesn't reduce NOX. HTH

Originally posted by harsanyj
I have posted this before, but I guess I'll do it again.

I was getting hight NOX on my 4.0L (like 2x the limit). Everything else was way below the limit. I had a relatively new cat (<3 yrs) and new 02 sensor and header. I tried cleaning the combustion chamber and it made no difference. Then, I went out and bought a 3 way cat from Napa and put it on. After that, I passed NOX with flying colors. I'm guessing the exhaust shop put on a 2 way cat which doesn't reduce NOX. HTH

I've thought about that, but if I touch the exhaust, I'll repalce the whole damn thing, I'm trying to start out small enough to make an improvement without spending close to $400 on a new header, 3-way Cat and a cat back system. I don't want to piece meal the exhaust together.

I know the other stuff needs replacing (plugs, wires, cap, yada yada), so if that helps improve the combustion properties, then great, and if it's enough to get it to pass then, that's even better.

I was gonna give you flippant reply to your laboring over your re-post, to stay within the flame realm here, but decided a good ol' :flipoff2: would be good enough...