Heres the info-
My 22re just failed its smog test all of my readings are average except nox its about 400 ppm past the cutoff on the 15mph test and 100 ppm on the 25mph test. The egr works and I pulled it off and I'm cleaning all the ports but there not plugged just a little carbon. I have a stock exhaust except a flowmaster muffler and I'm running 32" tires with 4.88 gears. Efi was cleaned last year and the motor was rebuilt less then 50,000 miles ago.I'm going to retard the timing and clean all the way back to the exhaust manifold.
Heres the questions-
I was told that running premium gas (91 octane) will lower my nox readings is this true? I'm on empty now so I was thinking maybe 4 gallons?

 

Higher octane does burn a bit cooler, which would lower nox a bit. Doubt you could get 400ppm out of it tho. Lean mixture would also cause higher temps/nox - do your plugs look worn with white deposits? If it's running lean, you might try cleaning your injectors. The best injector cleaners have a lot of polyether amine in them.

Techron and BG44K used to contain polyether amine, but they both apparently removed the chemical from their products. Techron still has some good stuff in it like xylene, but a look at the BG product shows that these days it's pretty much garbage - just petroleum distillates and mineral spirits:
http://www.bgfleming.com/products/msds/208.pdf
https://www.cbest.chevron.com/msdsSe...true&region=NA

So you're left with three products that I know of that contain a good percent of PEA: Red Line's excellent SI-1 Complete Fuel System Cleaner at 30-50% PEA:
http://www.redlineoil.com/msds/49.pdf

CRC's "Guaranteed to Pass Emissions Test Formula" at 25-35%:
http://www.crcindustries.com/faxdocs/msds/5063.pdf

And Gumout Regane - Kerosene and 30-40% PEA
http://www.e10gasadditives.com/files...ReganeMSDS.pdf

Add a bottle of one of those to 2/3 - 3/4 tank and burn it down to 1/8 or so (but no lower - bad for the fuel pump).

If the O2 sensor was reading too high it would cause lean mixture but that almost never happens; usually they read too low when they go bad. Check the VS spec on the air meter, that could cause mixture to be off.

Another thing that will help is retarding the timing, but with 91 octane I wouldn't go below 4 deg btdc with jumper set.

What kind of shape is the cat in? If it's older than 6-10 years it may not be doing what it should for your nox. Also many cheaper aftermarkets are 2-way catalysts which don't convert nox, instead of 3-way, which do.

 

Go over to the Marlin Crawler forums and look in the engine/drivetrain section, there is a thread there with lots of good information on how to pass smog.

 

Update: premium gas didn't help as far as I could tell it still failed. I had to fix (helicoil) two stripped holes on the head one for the dist hold down and the other for the egr valve into the head (that one was fun) I was approved for the cap program and it passed after a new o2 sensor and cat. The nox levels are now around 500ppm.