Hello again,
Looking for a "light" on this issue of the NOx test for my 93 Jeep Cherokee sport, 4L HO, 194k miles (yes it is old). Two years ago, when I bought it, it had a new CAT installed and it passed the smog test (done by the dealer in the dark alley). Now, it is doing double the limit in NOx, Can a new CAT fix it? do I need to rebuilt the engine? I am a little concern about engine temp; I change the radiator, fan clutch, belt and the thermostat (170 F) six month ago and if the engine is staying "too cold" it may not be burning all the stuff.
Any advice from the experts?
15 mph NOx 1163 ppm; 25 mph = 1181 ppm
Thanks

Check the o2 sensor..
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks Big Jim,
Although, due to the rains, I have not check the O2 sensor (l'll do it with the Autoxray) I have found some other things. Does anybody know what does it means "OBD Exempt"? the emissions sticker has that. I also learned that NOx is created by high temperature conditions in the combustion chamber and that engines have the EGR valve to control the temperature by recirculation of exhaust gases. My Jeep does not have one ! & the timing is not adjustable (it can be retarded by 2 degrees only, by law).
I am lost, any information will be appreciated.
Thanks

A bad 02 sensor will decrease or increase the amount of gasoline fed to the cylinders and cause heat from the lean condition.. hence increasing the noX.. I havn't had the problem but have heard many times of the 02 sensor causing the problem.
The timing is computer controlled and should be where ever the computer tells it to go.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

What are the typical readings of the O2? I get a jumping reading from 0.12 to .85 Volts and an indication that the engine jumps from rich to center and lean (back & forth). I was not able to tell when the engine when to closed loop, I was looking at the readings since I started the cold engine.
I will change the O2 sensor and compare the scanned readings.

Yes, NOx is created by high combustion temps, usually caused by carbon build up,(high mileage engines) BG 44k fuel additive works great to reduce carbon deposits.
On rigs where timing is not ajustable, motorvac service or 44k is the best solution.
Your O2 is working fine by those numbers, the swing from high to low is exactly what it should do.

Carbon increases temp by increasing compression ratio, like a diesel, they don't use spark to ignite the fuel, just heat created by very high compression ratios.

The best way to use 44k is to fill your gas tank normaly, add the 44k then drive (city type stop and go is best) till 1/2 a tank then top off again. This gets you 1.5 tanks with 44k in it. The worst is to add 44k then drive nothing but highway. 44k disperses the carbon when the engine is off and idling after getting to op temp.

Let us know the results and what you did.

NAPA and Carquest carry 44k $20 a can.


SD

Dagone SD is that a problem at altitude? I never have seen build up inside the chamber.. Lots and lots of it above but not inside the chamber.
hmmm maybe a little of it would cause knock and the knock would cause timing retard and the retard would cause even more buildup?
Anyway I have never seen combustion chamber buildup here in the flatlands.. Maybe just a bit but I'd think that was normal.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

You just hit the NOx nail square on the head.
Anything that increases ping or knock will create a NOx failure. Then when you get knock retard it all get worse.

SD

The problem is most likely the aftermarket Cat-Converter! I used to deal with this problem alot at the dealership I worked at. It usually happens on '91-'95 YJ's, XJ's and ZJ's with 2.5l or 4.0l engines. We would install a Mopar factory replacement cat-converter and fix the problem.

The state of CA. just this year addressed the problem of improper Cat-Converters being installed on vehicles. They usually are undersized compared to the factory part!

See this link:
http://www.arb.ca.gov/msprog/aftermktcat/aftermktcat.htm

And another one:

http://www.bar.ca.gov/80_BARResources/ftp/pdfdocs/ARSC-summer08.pdf

As of the first of the year,(2009) new replacement cat-converters MUST have a CARB EO# (Exemption Order), just like any other aftermarket part than can alter the emissions. It seems they found out that the low cost "universal" replacement cats skimp out on the Rhodium element in the converter that catalyzes the NOX. If you look at the last test result, right after you replaced the converter the last time, the NOX reading is probably pretty close to the maximum spec. The new cat-converter has to pass the same tests as the factory cat and has to be warranteed for 5 years. Expect to pay between $200-$400 for the new cat-converter.

You might try to see if your old converter still has a warranty left on it, they will have to upgrade it to the new style converter as it is illegal to install the old ones, now.

Hope this helps!

P.S. I'm a California certified Smog tech, and had worked for a local Jeep dealer as a smog tech there for most of the last 19 years. (I'm now in "semi-retirement" working for a University Fleet, still doing smogs though! <img src="/forums/images/graemlins/sleeping.gif" alt="" />)

Marty we are Happy to have you and your knowledge aboard..
Stuff like that is what we all need to feast our brains on..
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />