Why did my NOx go up?

[moochiemike123]

So, here I am, desperately trying to figure out how to fix my car... Ive gone through 3 smog tests, and failed them all. Here's how it went down.

I warmed up my car nice and good. Results:

http://i37.photobucket.com/albums/e59/moochiemike123/PIMG0100.jpg

Wow, I failed hard. So I replaced the cat (with a 49 state one, not Cali) and changed the spark plugs. Warmed it up again, and took it back:

http://i37.photobucket.com/albums/e59/moochiemike123/PIMG0101.jpg

Oh, hey, I failed again, but everything is down. CO is normal, HC is a little high, and NOx...NOx went WAY up at 25mph?!?! but down at 15? oh well, its still better...

So I'm close. I can taste it. I replace the 02 sensor, run through some G2P, change the oil, and put some alcohol in the gas (I don't think it really ended up doing that much). Warmed it up all good, and took it to try again...

http://i37.photobucket.com/albums/e59/moochiemike123/PIMG0102.jpg

Yay, so now my HC and CO are normal; nice and low. But my NOx is still high?

I cant figure it out. I guess the answer lies in the first test. Why were the numbers so drastically different? I don't think the cat is the problem, because it brought everything down... Maybe the plugs??? the second tests show closer numbers between 15 and 25mph, but its still high... I think I fixed one thing that brought down the 15mph NOx, but made something worse to bring them both high...

Anyone know what would cause high NOx at 15mph, but not 25???

[neptronix]

a 49 state cat is not adequate for california, nor is it legal if they actually look at your cats. you need a carb approved cat. they filter out much more stuff. Even though your NOX is high, you would probably pass with a california-approved cat.

at 25mph you are likely at a lower gear if you have an automatic trans.. that being more efficient, using less gas and such.

Your numbers are still very high for having brand new cats.

i put obd-2 california cats on my car with 155k miles on it and it blew numbers that made it look like a brand new car.

did you also replace both o2 sensors? i am not sure about the exhaust path on those motors but if you have two pipes going down into the cats, you probably have 2 oxygen sensors instead of just one.

[gripracer]

advanced timing causes extra NOx



A list of common causes of NOx related smog check failure:


1. As usual check the timing first. Advanced timing can cause extra NOx.


2. The next thing to check is the EGR system.This system is designed to reduce Nox. It consists of a EGR valve, vacuum hoses, one or more vacuum switching valves or solenoids. Its job is to reroute a small amount of exhaust gas back into the engine to help reduce combustion chamber temperature. Not all vehicles have an EGR system.


3. Next thing to check is the air / fuel ratio. If the vehicle is running to lean, NOx emissions will increase.


4. Some possibilities are a restricted fuel filter, low fuel pressure, vacuum leaks, oxygen sensor, load sensor such as a map sensor, air flow meter.


5. Check the cooling system. An extra increase in water temperature will increase NOx production.


6. A defective catalytic converter can also increase NOx. The Cat. reduces NOx that has already been produced.


7. Check to see that the air coming into the engine is not over heated. Some vehicles have a vacuum controlled air valve which switches the incoming air to hot air from the outside of your exhaust manifold.This should only happen when the engine is cold. If this system malfunctions and sends hot air all the time.Your Nox could go up. This system is called T.A.C. ( Thermostatic air cleaner )


8. There is another system similar to the one above called E.F.E. ( Early fuel evaporation ). This system routes hot air under the intake manifold. This helps keep the fuel in the vapor state. If stuck in the hot mode Nox emissions could increase and cause a Smog Check failure.


*Data obtained from www.smogchecksrus.com

[foamerdave]

put some alcohol in the gas :nono

Yes alcohol burns clean as can be. But it burns HOT AS HELL. This would raise your NOx ( till I read this I thought you put to "hot" of plugs in)
Also as said above some where vacume leakes and egr are spots to look. A new 49 state cat should pass for a few years at least.