Just picked up a 90 plymouth sundance and got it running great. I have to get it emissions pass in order to get it registered and it failed the Nox test. Here's the read out

Standard High speed(2628) Low speed(1668rpm)
HC 181 47 Pass 54 Pass
CO 1.18 0.13 pass 0.15 pass
CO2 -- 14.2 13.8
O2 -- 32.5 36.5
Nox(ppm)1313 1813 fail 2438 fail
Dilution% >6.0 14.3 pass 13.9 pass
Can anyone help me get this thing to pass emissions? I'm trying to turn this into my dailly driver and can't get it registered here in texas untill it passes emissions. (I don't know how they expect me to get it to the testing station legaly This is the most screwed up vehical registration state i've ever been in.
Any help to get this thing to pass would be apreciated greatly.

excess NOX is caused high combustion temp... Check EGR operation..

Do an online search for high NOX readings. You will find a bunch of info.

yeah, i didnt enjoy texas, but man, jersey was a hell of a lot worse!!

I love texas for the weather and food. Won't ever move back north. Just frusterating trying to get vehicals road legal here. I'm cleaning the intake and combustion chambers with "seafoam" and will back the initial timming off a little. Have to fix the shifter as one of the pivot bushings fell out and had to drive home in 2nd gear. I should just sell it to a non emissions area but now it has become personal and I will get this thing legal.

It's not difficult to register a vehcile in Texas. Millions of us do it every year.
I've even registered out of state vehicles without any problems.

Now that you've failed an emissions test you need to return to the same inspection station to pass.

Check the EGR as stated above and see where it gets you. Backing off the timing may help but I wouldn't go too far.

I assume this is a 2.2 TBI engine?

I hear you, I drove my Hemi Ramcharger to a shop last night to get fixed for the same issue, high NOx. It's tough finding anyone who will even LOOK at a non stock vehicle.

Robert

Well It passed and I'm not sure if they "doctored" the test a little or if what I did made that much diffrence.
Here is what I did. I ran seafoam straight down the throttle body. then I dissasembled the EGR and cleaned every thing. I found the black plastic "back pressure valve" was bad so I went to the junkyard and found one that worked. also the egr solinoid was bad but I couldn't find one of those so I just "bypassed" it for the test. then I backed the timing down to 2*btc from 12*btc. The Nox went from almost 3000ppm to 625ppm on the second test. So now I get to start driving my 25mpg car to work instead of my 12mpg truck.