I would bet it’s the cat. Mine failed the emissions test recently because of the NOx readings. I installed a new cat and it dropped the readings by 75%.

 

check for codes

 

You stated earlier that you added a few things to your tank to try to get it to pass...

It just occurred to me that some additives actually harms the efficency of the cat... Not that im saying thats your whole issue but it tends to clog cats up after all that stuff is burned and nox would suffer.

Are you using high test gas a couple of days before you go? Its helped me on a few of my cars that were borderline. They failed first and with some high octane fuel and some 108 additive it would sneak by... Just a thought and if it passed then you would have some time to get it figured out..

Just my two cents from experience..

 

Yea, I checked for codes and the only one was that the battery had been unplugged recently. I was running 91 octane but not the octane booster, I will probably give that a shot in addition to running some colder plugs. I just wish I could read the numbers to know if I was running lean or not.

 

Post nasal drip. My problem was the injectors dripping, not shutting off cleanly. Is your eng high mileage?

 

Yea, the engine has 161k miles on it. I measured the impedance of the injectors and it looks like they are 16 ohm which is outside of the 3-6 ohm range the book suggests is normal so they may indeed be bad.

 

x2 just move

 

How much denatured alcohol? It should be 20% + 80% 100 octane unleaded racing gas. 8 oz of "Heat" in a full tank isn't going to buy you sh__. NOx is caused by high temperatures in the cylinders. Both of the above fuels cool it off considerably.

A poster on a Volvo forum I frequent had the exact same problem you did, including having a new cat. The root cause of his problem was the new cat was wrong/bad/inadequate. He ended up getting a second new cat and that fixed the problem.

Here's a link for smog prep procedures.

http://cadillacforum.com/forum/showthread.php?t=3291

 

Have you tried slipping the test guy a $50?

 

in Calif setting the timing back 3 deg will get you a fail no mater what the emissions are

 

im glad SC dont have those checks

 

funny post

 

I wish that would work, I must not live in a shady enough area

I just ordered a new cat so once I get that welded in I will post back and let you guys know what happened.

 

For anyone intersted this site:
http://www.smogsite.com/calculators.html#lambda
Has a calculator that can interpret your smog results. In putting mine down it says my A/F is 14.7 which is ideal but may theoretically be a bit lean which is why I am gettin the NOx. Hopefully these results are just confiming it is the cat that is bad and not anything else in the motor.

 

So here goes.
I had the same problem. We all know that jeeps run fairly hot.. (as a general rule of thumb). . Nox appears in higher levels when the engine is hotter. What makes an engine run hot? The mixture. I think that Your engine, like mine is running too lean. Now what do all those additives do? They make the garbage in the exhaust burn up; and the sniff tester then gives you a cert. BUT they also get the engine very hot to do this too and that gives us higher levels of NO (stands for not ok---no really---Nitric Oxide). Don't use them day of --- not with a XJ, use them the tank before and drive HARD and Empty too!!! Then 1/3 fill on the day of with just 87 gas ( i also put in fuel injector cleaner 1 whole bottle for 20 gallons not just 7 but no octain boost). 87 gas requires more heat to burn more completely so of course it will have more gunk left behind in the HC and %CO sections but will be lower in the NO. ( if the % CO is higher then there is less space left in the exhaust gasses for the NO---very simmple terms---really sure how it works but it does) Remember too that 87 octain fuel works fine because of the slightly higher compression in these motors.
Also Check the O2 sensor. Check it for the wires that come out of it and see if the insulation has been burned away by the exhaust tubes. if it has, it is probably shorting out and not doing it's job and sending the correct info if any to the ECM. Replace at your discreation --- yes i know that it is only 8 months old but it only takes 10 mins at opperating temp to fry insulation. Then i cleaned the air filter (you have stock?). (. . .Granted I have a k&n and that don't help any- more air makes mix more lean if the sensor is not working. . .) Because you like me were prety close on the NO reading this should fix it. Clean enging day before. Burn cooler day of. Hope that you save $50-$60 by finding out if your O2 sensor wires are bad and reinsulating them with electritions tape.
If these don't work then you need a new cat. It will lower NO to around 300-200ppm WITH ONE CATCH it has to be a 3 way If the previous dude didn't use a 3 way and instead got a 2 way then it aint doing any thing to the NO levels!!!!!!!!!!!!!!

also the smog 8 moths ago didn't need the dymo just revving---found that out on the ca websit. selling smog is different than resmog. and last of all you can search by vin on the ca website to uncover the complete smog history of your vheical (if regestered in ThE PeOpLe'S RePuBlIc Of KaLiFoRnIa

pssss. On a rainy day when the shops are quieter then you can slip them a 50 and i have heard of it working. rainy days are slower and they need the business. But really if they take a bonus leave fast don't let them touch your car. or any thing in it that you want to keep..