I have a 92 ls400 with 247,000 miles on the clock and just recently failed a smog test due to NOx emissions being high. Everything else passes with low numbers except for NOx. The odd thing is it always has passed smog. The last time i had to smog it was in 2011 and it passed the emissions test with no problem even when I had a bad iacv leak in the power steering, I would get white smoke out of the exhaust when starting it up after sitting overnight. As long as I drove it for a while the white smoke would go away. Since then I have gotten the iacv fixed and it does not blow white smoke anymore. Other work I've had done on it was replace a cracked egr pipe and even more recently replaced the VSV which triggered to throw CEL code 71. I thought that was the problem but still does not pass.

Here are my numbers from smog test in 2011:
15mph 25mph
CO2. 14.9. 14.8
O2. 0.0. 0.0
HC. 38. 14
CO. 0.10. 0.06
NO. 24. 27

Now these are the results from 2013 when the Star certified test center was implemented
15mph. 25mph
CO2. 14.2 14.2
O2. 0.3 0.3
HC. 3. 3
CO. 0.03 0.05
NO. 665 678


Any help would be appreciated. I've searched the forums and come up with info on cleaning the egr but I'd just like a second opinion

Thanks in advance

 

if the EGR is working the way it should give this a shot.
http://www.lexls.com/tutorials/emission/egrfilter.html

 

run this through a tank of gas
http://www.amazon.com/CRC-05063-Guar.../dp/B000CIPUR8
make sure ur car is hot when u have it tested...drive it on the freeway for 30 minutes at 65 mph
make sure ur oil is changed and u have tuned it up..it will pass providing u dont have vacuum leaks or a check engine light on

 

I'm with PD, check the EGR system. NOX is usually an EGR related issue when it shows up.

 

Thanks for the info I just cleaned out the mnudulator filter but I don't want to get it smogged just yet it having it fail again. The number just seems so high from what it was 2 years ago. Also I just remembered that when I got it smogged in 2011 I had a cracked egr pipe when I had it tested, and it still passed with very low numbers. If its not the egr system what else could it be. Has anyone had any experience with high NOx readings and fixed it with a certain egr repair?

 

X3 on the EGR system.

NOx are caused by high combustion temperatures/pressures and the EGR cuts back significantly on them.

 

EGR as well. is the pipe still cracked? you need to fix that first before proceeding.

 

Check the vacuum lines that actuate the EGR system. Many of the flexible hoses by this time are pretty hard and brittle if not leaking in some small way. Buy yourself about 20' each of the appropriate sized vacuum hoses and start replacing them.

Tip: don't try and yank them off the plastic fittings. These are equally brittle. If they don't slide off with a bit of soapy water, cut the hose off. This is the result of my applying more force
https://www.clublexus.com/forums/ls4...e-fitting.html

 

Yes the egr pipe has been replaced, the odd thing is that it passed the smog test even when it was cracked, I had it tested not knowing it was cracked and it still gave me the readings I posted first (2011 smog test).

 

A mechanics is telling me that it could be my catalytic converters, can this be a possible reason also? I do have a leak in the front crank seal that drips down and gets on the front cats, and also when I took it to smog I saw white smoke coming out of the exhaust when it was on e Dyno

 

I just cleaned out my egr, it was caked with carbon deposit. Hopefully it will pass smog

 

Still didn't pass after I cleaned out the egr valve and passages. Numbers of NOx ppm did not even make a difference... Any thoughts?

 

did u do what I suggested? obviously not

 

I did, ran through a tank of 91 from chevron with the croc g2p. And even cleaned out the egr valve and passages from the manifold. nOx measured no difference

 

The EGR is usually the culprit. Vacuum pressure is ok to actuate the valve? Beyond that it begins the usual EFI hunt and in those instances, a code is thrown.