Hi, I'm having trouble passing CA smog with high NO levels. First had car tested around in May, failed with high NO at 15 mph, passed at 25.

That test results: (Max = maximum allowed emissions)

15 MPH- FAIL
HC: 26 (55 max)
CO: 0.02 (0.5 max)
NO: 937 (437 Max)

25 MPH- PASS
HC: 14 (39 Max)
CO: 0.03 (0.48 Max)
NO: 204 (724 Max)

I had just gotten the car back then. Since then I've done all basic maintenance, I've changed all 3 O2 sensors, I've replaced the PCV hose which had a leak, and I've cleaned the EGR Valve (along with the TB, MAF, and IACV on the way, per the directions on this forum. New gaskets for all)

I failed again today, after the above listed maintenance and the 3 month difference, my new results are even worse:

15mph-FAIL
HC: 49
CO: 0.0
NO: 1751

25mph - FAIL
HC: 52
CO: 0.0
NO: 1820

Smog tech doesn't really know what could be wrong as there are no check engine codes. Things that have been suggested to me are EGR tube (which I cleaned), and the Cat, but the smog tech told me that if the Cat were bad all of my numbers should be worse, instead of just NOx.

I'm pretty clueless as to what to do, so any suggestions, ideas, help, or even just experiences in this area I'd be really grateful for.

Thanks for reading!

P.S. I've tried the "Carb Cleaner spray on intake hoses" trick to look for vacuum leaks. I didn't find any obvious ones, but I don't feel super confident in that area so who knows.

 

High nox is is directly related to high combustion temps. Clean you EGR tube first off, do you have functioning EGR? Could be a cooling problem too, is your engine running hot?Running lean would do it too, but you don't have a code so I'm guessing no.

 

You can install a water vapor injection system before the throttle body. Tends to lower combustion temps and pollution.

Very cheap to make, here's a basic schematic.

http://journeytoforever.org/biofuel_...earth/me3.html

If you used a 4" pvc pipe with an endcap and topcap, a 4" diameter round airstone from petsmart you could place the airstone directly on top of a 3/4" air stream inlet pipe inserted horizontally through the base of the 4" pipe with a check valve outside the on the outer end and the inner ending in a T with hole drilled into it at base of the 4" pvc pipe. On top of that you can place set of drilled pipes as spacers to prevent the airstone from moving up under pressure. Placing your vacuum inlet at the top of the container.

That's be a touch better and safer than the mockup in the article and would provide larger amounts of water/alcohol vapor.

Been shown to work on fuel injected too.

 

Put a bottle of, "guaranteed to pass" in the fuel tank.That will lower your nos,you'll pass the test.

 

When was the last time you changed your plugs? That would help and make sure you are using premium fuel. People don't realize the components of 87 octane is garbage for our compression engines.

 

Best in CA is 91, and at 3.59 a gallon..... its almost worth going 87 =(.

 

I cleaned the EGR tube only a few days ago before I got it retested, I got it as clean as I could. Didn't help my NO levels, in fact theyve risen since a couple months ago . Pretty sure I put everything back together tight, new gaskets, etc

Thanks for your info, while I don't doubt you're on to something and I appreciate your insight, I'd personally prefer if I could pass with more conventional, "stock" methods

Never heard of this. Looked it up now, I'll give it a shot if i can find it. Thanks.

Plugs are new and in great condition, actually. I only use premium fuel, which as cartman says, here in CA is 91 octane

Thanks for the replies so far guys.

 

If the plugs are new make sure they are gapped correctly, misfires can contribute to high nox.

 

did you try testing the egr?

 

I've cleaned the EGR pipe/tube, but I don't know how to test the valve

 

MY CAR JUST FAILED TODAY I NEED A NEW CAT THAT COULD BE YOUR PROB ANY 1 NO WHERE TO GET A CAT THAT WILL PASS CA SMOG

 

I know that NOX is created by extreme combustion tempratures. With what you've done I don't have much to advise.

A friend of mine from Schneider Cams told me something the other day. He runs 9 parts denatured alchohol to 1 part gasoline in the tank, just a gallon or so of it in a nearly empty tank. The car will run like **** since it's not tuned to run properly on alchohol but it supposedly runs extremely clean for the pipe test. I don't know if it would cause a CEL, but he's never had a problem.

By the way I'm not responsible for any damage to your car if you try this. It's something to research and look in to though. If anybody else has heard of this or knows anything about it please speak.

 

I know how you pass it, move way the hell away from California.

 

I'm willing to bet that its your O2 sensors that are at least contributing a good amount to the high NOx. I had the same issues and new ones helped me pass. Should be about $40 each for OEM plug in ones. 2 sensors are the same if i recall before the cat converter. One more sensor downstream from the cat. If you're limited on budget, replacing the 2 upstream ones would be the most beneficial.

 

Thanks for the new suggestions. Unfortunately I've already changed both upstream AND the downstream o2 sensors, before I even took the first test . I acutally had a check code for the left upstream O2 sensor before the first test, so that was a no brainer (I just went ahead and changed them all)

 

Do Not Do This!!

 

Sorry! I must have failed to see that you had already changed them in your initial post. My bad

 

if 91 is 3.59, 87 will be 3.39. saves you a whole $3.70 per $60 tank. nice math skillz genius

 

I also say stick with the 91 octane, its barely more expensive and is SO much better for the engine etc. After all its what nissan recommends "for top performance" that is.

 

And why I might ask? Works great on my max.

 

change your cat i did and i past like a new car. my nox was way higher than yours

 

I heard the cost of catalytic convertors have gone way up. Also, thefts of catalytic convertors are on the rise because of this. Crazy!