Failed NOx with 2.53 with the limit at 2.5. Kicker is when I looked at the paperwork the engine size says 1.8/4 which I have the 2.5/6. Are larger NOx ratings given to bigger engines? Couldnt find it anywhere. Would call the shop but closed till Mon.

Answer is no;
TABLE ATransient Loaded – Mode Emission Test Standards in Grams Per Mile

Hydrocarbons Carbon Monoxide Oxides of Nitrogen

Cars
1996 and newer 0.80 15.0 2.0
1991 – 1995 1.2 20.0 2.5
1984 – 1990 2.0 30.0 3.0

1. Was your car warmed up all the way? Did you take it for a drive at speed on the highway before the test?

2. I thought mass was not doing these tests anymore...Did they put it on the dyno? Or was it just a standing idle Tail Pipe Emissions test?

1. operating temp no highway
2. Tail Pipe

Redo will be next sat with a more thorough warmup and some 93 in it.

Need to get it hot, how old is the O2 sensor, might be worth while doing seafoam in the tank and doing a O2 sensor.

Gotta drive it on the highway and then go.

leave it running when you get there too

Getting it hot won't likely help with NOx. NOx is more related to combustion chamber temperatures. Hydrocarbons are burned up in the cats when they are warm, so fixing them is done by ensuring the cats are hot.

I'm in the same boat (one tenth over on NOx, everything else fine) and just replaced my spark plugs and coil packs, hoping that will make for a healthier atmosphere in the combustion chamber. The combustion chamber being too hot is what causes the high NOx. You can try replacing the O2 sensor if you haven't done so - it's possible the one you have is causing the engine to run too lean. You can also try Sea-Foam and see if you can remove any carbon buildup in the combustion chamber.

I've already failed 4 times though, trying to run at different temperatures, before and after the O2 sensor replacement, etc. My catalytic converter's very new already (~2 years). I really hope I get it next time, since I got pulled over for failed emissions on Friday and the state cop was nice enough to hear me out and believe me that I was trying. Not sure how long I can expect that luck to continue.

By the way, in October, MA is dropping the sniffer test altogether. Cars from before the OBD-II days will just have safety tests and no emissions.
-N

To add to the conversation my results. I got my 5th emissions test today and passed with flying colors. Every metric was way down below the limits and way down below what it was before.

The best I got before was: 0.56 on HC, 8.89 on CO, and 2.63 on NOx. The NOx failed me. Those others had come down a bit with the O2 sensor and the O2 sensor also brought the NOx down from its original ~4.5.

This time I got: .11 on HC, 2.82 on CO, and 0.86 on NOx. That's way better than I expected and is the last time I'll ever have to pass an MA emissions test.
-N

These old engine burn clean if you keep up with proper maintance and after you added the O2 sensor did you mileage start to creep up?

These old engine burn clean if you keep up with proper maintance and after you added the O2 sensor did you mileage start to creep up?

My numbers are HC 0.28 CO 3.64 NOx 2.53 so overall pretty good just off on the NOx. Last fall (before storage) was new fuel filter, air filter, plugs, valve adjustment. Cat and O2 sensor are two years old.

We will see this week if I sneak by.