My LO3 automatic failed emissions again. NOx gases were too high. Any suggestions? The engine temp hung around 220* the entire time. My theory is that the thermostat may be going. What do you guys think?

 

Has everyone gone home?

 

Bad O2 sensor perhaps?

 

first off, I don't have emissions, but I'd try putting the stock chip back in, and set the timming to 0*

 

I'm sure someone will correct me if I'm wrong, but NOx is reduced/controlled by EGR isn't it? Do you think your EGR valve could be shot?

 

Here is what I know for sure:

EGR valve replaced last June '01 (couldn't pass emissions then either).
Catalytic Converter replaced las June '01.
Checked for trouble codes and found none.
High NOx usually means Temperature too high.


The day I had the car tested I got caught in stand still traffic on the interstate for about 30 minutes. The temperature gauge hovered around 220*+ until I had it tested. The test for higher RPM band and lower RPM band. I passed one of the two which to me seems to indicate a engine temp problem. Help me out here guys, if the EGR valve or O2 sensor was bad, it would have failed both RPM tests?

I have installed a new 160* thermostat and plan on re-installing the factory chip (timing is still set at 0*) and retest first thing Saturday morning while the car is still relatively cool.

 

It shouldn't be getting that hot! 180max unless you've got a/c on. A broken thermostat will take longer to warm up, car will run like crap and you'll have high NOx fumes. My car failed once for high NOx fumes so I ran a bit leaner and had my car tested when the temp was at 190 intstead of the 220. I don't have EGR and EGR cools down the combustion so you won't have as high NOx. Definatly make sure you EGR is working, keep the eprom in, and fix your cooling problems!!

 

I failed my smog check this week as well for NOX, initially 1700-2100 PPM at 15 & 25 mph tests. I have a little over 2 years and 15K on the Random Technologies cat. The car also has SLP 1-5/8" headers and a 3" intermediate pipe. I swapped in a stock 195 t'stat for the 160 as well prior to the first test. We tested the EGR but couldn't get it to open. The EGR was new 2 years ago from my last smog check time. I also had a custom programmed chip in for that test. Afte the first test we went back and looked at the programming and found the timing was bumped by roughly 10 degrees in the RPM range they run the test at. We replaced it with stock chip. Swapped back in the 160 t'stat, modified the EGR (Drilled open the orifice) then re-tested. Levels dropped to 1100 PPM, still too high. The tech told us the cat was bad. My car puffs blue smoke on startup (bad valve seals). This has coated the cat. We replaced the cat and also added a small restriction (2-1/2" reducer) in the outlet side of it for more back-pressure. Re-tseted and it passed with flying colors. NOX in the 200-400 range. Yours may have similarly fouled the cat with oil as well. I'm good for two years now, but my ultimate fix is either a rebuilt Vortec 350 or Vortec heads on this engine. We'll be scrounging up parts soon. Keep the engine running before the test to keep the cat hot. Good luck. Lon

 

that temp isnt too hot, its normal, my fans dont even kick on till 220.

 

It passed Saturday afternoon!!

I put the 160* thermostat in it Thursday evening and drove it to work Friday. The temp never climbed above 170*. Dropped it off Friday evening to be retested. The tech unplugged the advance, which made it run like crap, but it passed.

Thanks for all the ideas.