My other car failed emissions (Massachusetts).

The limits are:
HC (grams/mile): 2.00
CO (g/m): 30.00
NOx (g/m): 3.00
CO2 (g/m): n/a

My numbers were:
HC (grams/mile): 2.22
CO (g/m): 10.50
NOx (g/m): 2.10
CO2 (g/m): 328.23

Obviously failed for HC. The explanation on the sheet from the inspection station was: “Primary systems that affect HC (which is unburned fuel) include mixture control, ignition, and exhaust after treatment. O2 sensor, ign. Components, retarded timing and fuel injectors/carburetor are common problems. Check MAP/MAF, TPS, RPM, and CTS sensors. Also, deterioration of vacuum routing, intake preheat and catalyst should be inspected.”

My modifications are Split Second MAF conversion, higher flow airbox, K&N filter, aftermarket chip, hotter plugs, center section with silencer delete (cat retained), and stock muffler. I had just changed the oil a few days before the test.

The SS A/F ratio was about 14.4 – 13.2 from 0 – 4,000 RPMs, 13 – 13.2 from 4,000 - 6000 or so, and then drops to 12.8 – 13.1 above 6,000.

Over the winter the car was stored with 93 octane and stabil. I had used ½ tank of gas and filled up with 93 an hour before the inspection. The car was run for about ½ before the inspection, shut off while I removed the window tint applied by the previous owner, and then fired up for the emissions test.

My plan for changes before I head back in to get it retested is:
1.new stock plugs
2.new wires (no idea if or when these were ever changed)
3.new cap and rotor (again no idea if or when these were ever changed)
4.fill up with Sunoco 104

I am also planning on getting a new coil. I have searched and see no drawback to getting a MSD coil. Any issues with the MSD coil before I place my order?

Some of the advice I have received has been:
1. tune the SS so my AF ratio is 14.7 - 15. This will obviously lean it out, but will it increase my NOx?
2. don't run the 104 because its harder to burn. This is contrary to what I have read elsewhere. What's the scoop?

Thanks,

Craig

If your AFR is close to dead on at stoich, you should still pass NOx while reducing HC. 104 octane does take longer to burn, and effectively, you get hotter exhaust if timing hasn't changed (since the mixture is not finished burning yet). All of this is done to keep the cat at optimal operating temperature. Ethanol blend might be a better choice than 104 octane though

My other car failed emissions (Massachusetts).

My plan for changes before I head back in to get it retested is:
1.new stock plugs
2.new wires (no idea if or when these were ever changed)
3.new cap and rotor (again no idea if or when these were ever changed)
4.fill up with Sunoco 104

Have you thought about replacing the O2 sensor? That would be my first suspicion.