NOX Question. Failed inspection.

[mrneg9]

I was searching around and read other posts about failing for emissions because of Nox. I own a 1990 240sx with around 125,000 miles. It has a cold air intake,headers and full 3in. exhaust from the headers back. Went to the inspection station here in NJ. Car passed with flying colors other than the NOX. Normal was around 1200 I came in at 3000. After reading some post I went and checked my EGR valve. It looked ok but then I noticed a hole in the vacuum line that went from the EGR to the bottom of the other valve (I think its called egrc-bpt valve) Do you think this vacuum line was my problem?

[h.240]

There is a high chance that is the problem since the EGR's main function is to help with NOx emissions.

[Cone Junky]

Definitely fix the obvious issue of the broken vacuum line. The EGR operates via vacuum, so it's very important.

If you have access to a vacuum pump, I would manually open the valve while the car is idling. It should make the car stumble and most likely stall, which means it's working. If not, you may also have clogged EGR ports in the manifold.

Also make sure there are absolutely no exhaust leaks before the catalyst. ANY oxygen let in before the cat will dramatically increase NOx.

[mrneg9]

Fixed the hose lowered the timing took it back to the state inspection and it still failed for high nox. 1200 is allowed.It was about 3200 first time. This time at 2000. Going to try some of that guaranteed to pass stuff. Let you all know what happens. D

[spooled240]

make sure your EGR isn't clogged. A bad EGR valve will cause high NOX

[Cone Junky]

Fixed the hose lowered the timing took it back to the state inspection and it still failed for high nox. 1200 is allowed.It was about 3200 first time. This time at 2000. Going to try some of that guaranteed to pass stuff. Let you all know what happens. D

I'll tell you right now, it won't work. Make sure you read the complete label and disclaimer before wasting your money on that snake oil.

I would suggest (again) to check if the EGR is functioning. The main purpose of the EGR is to reduce NOx.

[mrneg9]

Went out today checked all the hoses again. Put my finger under the EGR valve and pushed. Car wanted to die out. Let go and and the EGR opened up and motor ran fine. Does this mean the EGR is working ? My friend that I got the car from informed me that it would not pass for him also due to high NOX. He replaced the CAT and that made no difference. He had to pay a private garage to pass it. Do you think changing the Oxygen sensor would do anything for the high NOX. I want to correct the problem so it passes the State Inspection as I do not feel like paying someone every two years for a sticker. What a pain in the A** this is turning into. D

One other thing. My friend seems to think that the larger cold air intake and free flow filter is making the car run leaner. He said that maybe it would pass if I was to close up the air flow at the filter. I don't think that would make a difference as the MAF would adjust for the air flow increase correct ?
Modified by mrneg9 at 11:15 PM 11/11/2008

[spooled240]

try pinching the vacuum line leading to the diaphram that opens the EGR valve and see if your rpms drop.

high nox are usually caused by two things:-High temperatures, which is caused by a lean mixture and/or a bad EGR valve-High combustion, usually not the case unless you did a n/a build with high compression.

The cold air intake will not cause high nox, I still think it has something to do with your EGR or a leak in a vacuum line or something simple..a small air leak after the mafs somewhere will lean out your engine as well.. what ever you do, replace O2 sensors and such as a last resort.

[the converted]

Have you double checked your timing? That can cause issues too.

[Cone Junky]

The problem that put my NOx over the top was an exhaust leak right before the cat.

I cleaned my EGR and ran fuel injection cleaners through my intake to drop my NOx from 1800 to just under a 1000 ppm. Unfortunately my limit was around 800 ppm. So a close inspection revealed that the brand new cat that the PO's put on to pass was not completely welded. After 10 minutes with my MIG, the NOx dropped to less than 200 ppm. Any oxygen put into the exhaust stream before the cat will skyrocket your NOx levels too.

[mrneg9]

Well guys after 4 times I finally got her to pass. You wont believe how. Turned the timing all the way down and took duct tape and tapped the air filter up until there it just about ran. Car had no power and took a while to reach speed on my way to the state inspection station. Results: I needed under 1378 to pass. NOX came in at 533. Before i was getting readings over 3000. The problem I think was that the mass air flow sensor will only adjust so much and I was dumping so much air into the motor it couldn't compensate. Any way afterwards got down the road took the tape off and turned the timing back to stock and bam shes a mean little machine again. Looks like in two more years I will be doing this all over again. Hope this helps. One more thing that guaranteed to pass stuff did not work at all like you guys said. Ran it with an entire tank of gas and my Nox readings were actually higher. Later,D

[pigmouse]

Just FYI if somebody is searching this thread...

I had similar experiences. Cleaned EGR, checked timing, replaced cat. Still failed. Found out months later that my MAF self-cleaning function was not 'functioning'. Replaced MAF and it passed.

This was a z31, but I believe they have roughly the same MAF system as the s13. If the hotwire is a little dirty, it will not register all the air that is actually passing it, and therefore will not signal for enough fuel = lean run = high NOx.

Autoparts stores now sell a MAF cleaning spray, which they didn't back when mine was failing. Might be worthwhile to try.

Oh, and the 'guaranteed to pass' crap DOES NOT WORK. Those people should be sued. If you really know how emissions and engines work, you realize why it doesn't. But I too wasted money on it once.... They prey on our hopes and dreams!!!!