My jeep failed the 15 mph NO test for CA SMOG.

I have a 95 YJ with 4L I6 5 speed and about 86k. It has passed every year prior to now. It passed every other part of the test including the 25 mph NO test. I gave the jeep a tune up including new plugs, cap and rotor, oil change and clean air filter with fresh gas and failed again. The jeep appears to run well, no smoke or smell and starts right up. I think it might be timing but haven't had a chance to check yet.

Does anyone have any ideas? I'd prefer not to bring it to a shop if I don't have to.

Anyone have any experience with the additives that claim to guarantee passing (i.e. BlueSky)?

Appreciate any help.

Octane booster. Get it good and hot before you take it in.

Octane booster. Get it good and hot before you take it in.

Thanks for the quick reply.

I drove it around for about 15-20 minutes at highway speeds before bringing it in. Would a higher octane gas be better as well? Plus octane booster?

Thanks again.

Went through this a few years ago with my 94, researched a bit on the web.

Run the lowest octane fuel the 4.0 will run on

Get it good and warm (drive 20 miles or more)

Make sure you have the stock thermostat, cooler thermostats don't help you.

Went through this a few years ago with my 94, researched a bit on the web.

Run the lowest octane fuel the 4.0 will run on

Get it good and warm (drive 20 miles or more)

Make sure you have the stock thermostat, cooler thermostats don't help you.

Thanks for the advice.

Ran just the plain reg unleaded and have the stock thermostat but still no good.

So I'm trying to figure out what else it could be.

thanks

if your running larger tires.. swap to a set of 235/75/15's.. Seriously

Are you still on the original O2 sensor? If yes, yopu might want to replace it.

if your running larger tires.. swap to a set of 235/75/15's.. Seriously

X2

and make sure the egr is functioning properly if equipped

Why would you run the lowest octane? When I had my old CJ7 our mechanic always said to run high octane with a little boost. Whenever it would fail I'll put a little bit of race gas in the tank and it would always pass.

I had a rep from Trick racing fuel tell me that the 100 octane unleaded will help with emissions because it is VERY refined. He said it has way less "crap" in it than pump gas. Maybe that is why the race gas worked for you. I haven't had the oportunity to try it yet myself.
Travis..

I appreciate all of the help and replys.

This jeep just passed 2 years ago in the same exact condition it is in now with the exception of some new dents and scrapes. Same tires, egr, O2 sensor. It passes everything at the 25 MPH test and only fails the NOx at 15 MPH. I've only driven the jeep offroad the past couple of years so it was still on the same tank of gas the first test. Second test, fresh gas and tune up.

I've heard the gas things both ways. The guy that I go to for the test has told me I can keep testing as many times as I want for only $20 each time but my reg expires this month. I've tested it twice and the second time after the tune up the NOx levels were higher. I know the fix has got to be something simple just don't want to keep making stabs in the dark. I know someone here is smarter than me with this crap.

Any other ideas? If not, I think I'll check into a new O2 sensor, egr and maybe try the higher octane full with some booster.

Thoughts?

Thanks again

borrow a set of tires and take it down and get it tested. Over time the cat becomes less efficent, and the larger tires put a bigger load on the motor at lower speeds.. Seriously. Dont spend any more money on it than you have to.

An engine that has been used under light load (wheelin') with a fresh tune is gonna have the #s way off. You need to go out and do some serious hard WOT with it to burn off the deposits in the combustion chambers. I did this with my grandmas car, big clouds of brown shit out of the tailpipe. You should also check your egr since you say it has one. It may be partially clogged causing it to be ok under certain rpm/load conditions and not others.
Travis..

you may want to read up on your emissions laws. You may be suprised @ how they seem to help out the big corporations.

Being in that position suks,
have a 94 that i requested a pre-test on and the shop just ran it. it failed. its now considered a gross polluter and of course the states answer is to crush the vehicle (or pay non-op fees until condition is brought up to speck and having to deal with a smog refree). Wich in turn if crushing is paid for by a big corporation, earns them "credits" allowing them to pollute. yet the average joe has to pass all the tests....
Its bullshit with no end.

I've had NOX problems with 3 jeeps in the last 2 years. Here in cali you need to replace the Cat with a new OBD2 Cat. It should cut your NOX numbers in half

I really don't want to go and spend $200-$300 bucks on a new Cat if I don't have to especially since the Cat that I have on there is only around 5 years old (I've already replaced the stock).

Anyone know what a new O2 sensor runs? Is that a dealer only part?

I think I'll try the high octane gas and octane booster to see if I can blow any carbon deposits out and then check my egr and O2 sensor (depending on how much it costs).

I'll let you know how it turns out. Thanks.

Last year I had a hard time passing smog on my jeep, same issue with high NO. The owner of the smog station told me to de-carbonize the engine with water.

I can't remember exactly what I did, but basically I ran a small hose from one of the vacum fittings on the intake manifold, reved the engine up, and put the hose in a gallon of water. The engine sucked up the water and ran rough, I had to adjust the throttle to keep it running (guy told me to keep it above a certain RPM, but I don't remember now). Took it back to the smog place and it past with no problems.

Last year I had a hard time passing smog on my jeep, same issue with high NO. The owner of the smog station told me to de-carbonize the engine with water.

I can't remember exactly what I did, but basically I ran a small hose from one of the vacum fittings on the intake manifold, reved the engine up, and put the hose in a gallon of water. The engine sucked up the water and ran rough, I had to adjust the throttle to keep it running (guy told me to keep it above a certain RPM, but I don't remember now). Took it back to the smog place and it past with no problems.

My Dad told me something similar. He said to to let the intake suck in a water mist to help clean the carbon out of the chambers. Might give this a try as well. thanks.

When I was having trouble with an old 89 wagoneer... I did a complete tune-up, checked the timing, put a better coil (MSD Blaster) on there with an MSD Dist (just be sure to put the CARB Legal Label in the engine bay someplace)...

Assuming I was running better (cleaner) I also ran a fuel cleaner and oil cleaner through the car, gave it an oil change, then used one of those "Pass Smog or Your Money Back" bottles that they sell at any autoparts store. You have to run down a full tank of gas tho.

This site has the tips above as well as a link to a cleaner...

http://www.smogtips.com/six_things.cfm

Passed with no problem. I was even missing a little bit of the OEM emissions system, but no one noticed. I think the cleaning out old junk and having the car hot are key.

X3 on the tires...

When I was having trouble with an old 89 wagoneer... I did a complete tune-up, checked the timing, put a better coil (MSD Blaster) on there with an MSD Dist (just be sure to put the CARB Legal Label in the engine bay someplace)...

Assuming I was running better (cleaner) I also ran a fuel cleaner and oil cleaner through the car, gave it an oil change, then used one of those "Pass Smog or Your Money Back" bottles that they sell at any autoparts store. You have to run down a full tank of gas tho.

This site has the tips above as well as a link to a cleaner...

http://www.smogtips.com/six_things.cfm

Passed with no problem. I was even missing a little bit of the OEM emissions system, but no one noticed. I think the cleaning out old junk and having the car hot are key.

X3 on the tires...


I saw that site that's why I was asking about the additive.

I've already done the tune up so i'll just do a combo of the above, although I checked and no egr on my jeep, and try again.

Thanks again.

got this from naxja

De-Carbon Engine procedure
The AMC242 is an agreeably low-compression engine - but the 1991-up versions lack the knock sensor that the RENIX (1987-1990) had. I'd suspect carbon deposits - and here's what I'd do...

1) Crawl under and disconnect the catalytic converter at the four-bolt flange (that should still be under there. Find some way to disconnect it, or you're going to have to replace it outright...) Make sure that the converter inlet is not directly in line with the end of the downpipe - cover it if necessary.

2) Disconnect the air intake hose from the air filter box. Have the open end held up by the neck on the box, so you can look into it.

3) Start your engine, and have a helper hold the throttle at about 1200-1500rpm.

4) Have a spray bottle filled with PLAIN WATER (distilled is best, R/O filtered is acceptable. Do not use tap water! It will leave mineral deposits in your engine...)

5) At intervals of 45-60 seconds, spray one full squeeze only into the open air intake tube.

6) Repeat until you no longer get black clouds out the disconnected tailpipe.

7) Re-attach catalytic converter at flange, using a new gasket or RTV Copper.

What Happens:
The fine mist of water travels down the intake into the combustion chamber, where it is soaked up by the carbon deposits. "Flash" combustion temperature average 1800*F or so, so the water will be "flashed" into steam. You are literally steam-cleaning the inside of your combustion chambers, and that black stuff coming out your tailpipe is the carbon that used to be in your chambers. You will not harm your engine if you keep the water use in moderation (Note the intervals and conditions above - but they're easy.)

Why It Works:
The water gets absorbed by the carbon deposits, and then flashed into steam. The expansion of the water being "flashed" literally blows the carbon right off of the surface where it was deposited, to get blown out the tailpipe.

You can safely do this every couple of years without harming anything - I do.

The best solution is to quit using cheap fuel (the most common cause of carbon deposits,) but that's difficult to do these days. I do this shortly before each smog check - the State of California gives me a reminder of the time to do it every two years... Converter flange gaskets are just something I buy in bulk (along with thermostat gaskets - you never have one around when you really need one...)
__________________

Light load NOX failures are generally due to too lean of a fuel mixture and excessive combustion temperatures. It may be due to carbon deposits, but you should be able to tell by looking at the O2 content and CO content from the analyzer.

If CO is very low and O2 is very high, you are looking at an overly lean condition.

I believe that if you had enough carbon build-up to screw up low load NOX, you would have the same issue at high load.

You want to check for vacuum leaks first. A fuel injection cleaning would be the next step. Lastly, I would look at the O2 sensor. If the O2 sensor heating element fails, it may not be getting warm enough at low rev's to register correctly.

-Old Army

EDIT: I just noticed that you mentioned the timing. Check that first. It will give you high NOX if its too advanced at low RPMs, but NOX will likely get better as the advance is backed off at higher revs.

I have Jeep Wrangler,l. It has 105,000 miles. It recently failed California SMOG test (emission test). It Failed for NO (PPM). It failed because @15 mph, 1777 RPM, NO (PPM): MAX allowable=467 and MEAS (Amount measured)=1403. My engine light has been on about a month prior to the SMOG test.

Here are some of the info from SMOG test report:

@15mph, 1777 rmp;
CO2% = 14.50, O2 %=0.15;
HC(PPM) Max=61, AVE=9, MEAS=12;
CO% MAX=0.54, AVE=0.02, MEAS=0.43;
NO(PPM) MAX=467, AVE=57, MEAS=1403;
Result = FAIL

@25mph, 1812 rpm;
CO2%=14.7, O2%=0.04;
HC(PPM) MAX=45, AVE=7,MEAS=7;
CO% MAX=0.53, AVE=0.03, MEAS=0.45;
NO(PPM) MAX=754, AVE=50, MEAS=742;
Result =PASS

Note: MAX=Maximum Allowable Emission, AVE=Average Emission for passing, MEAS=Amount measured

Just to give you an idea, my friend told me when he had a looked at the readings and the good news is that the HC and CO amounts are good but it rules out a lot of things like a Jeep catalytic converter (http://www.aftermarketperformanceparts.com/jeep-catalytic-converter.html) failure and engine problem. He also mentioned that high NOx readings are caused by a malfunctioning EGR system, hence, I said that the check engine light has been on but to really help my Jeep, he told me that I need to know what the trouble code is. But he was confident it is related to the EGR system(probably a DTC PO401)... i know for fact that egr system is designed to reduce combustion chamber temperatures which cause a reduction of the NOx gases, if the egr system is not functioning the combustion temperatures will rise and cause the check engine light to come on, the computer monitors the egr gas temperatures and if there is not enough gas flow will turn the light on. Anyway, He suggested to have a repair shop test why it is happening, to test the system requires a vacuum gauge and pump, a scantool and someone that knows what they are doing... Well, gonna check first the code at autozone.. I heard its free and see how it goes... Good luck!!!