I was having trouble passing emissions on my car in TN. They do a sniffer test here, and I didn't have any cats.

My exhaust is a Megan Racing DP & MP, and the racing beat catback.
So obviously I failed.

HC: 646 / 220
CO:2.14% / 1.2%

I didn't want to spend money on a cat if I didn't need to, so I looked around the forums and found people talking about random tuning and stuff.
So I grabbed the PFC and drove the car hard, went to the testing place and started leaning out in the temp settings page.

Results were:
HC: 672 / 220
CO: .8% / 1.2%

Interesting.
Time to get a cat.
Got myself a midpipe with a cat and to the tests I go.
With a cat and the same method as before I leaned out the car.

HC: 233 / 220
CO: .3% / 1.2%

Are you kidding me!? At this point I was a bit mad, so I went online stated looking on how I could get the 13ppm of HC down. I found a ton of results from all kinds of car forums, and almost all of hem said, make sure you tune your car properly, DO NOT lean it out. Ok fine, before I was a ton of money lets set it back to proper daily drive tuning.

HC: 87 / 220
CO: .38 / 1.2%
Amazing.
So this was a pretty interesting group of tests for me.
Don't know if anyone else finds this useful, but my mechanic brother surely did.

 

good post. thanks.

we dont have sniffers in NC anymore. its only a safety test 96 and older

 

^ Same as NY

 

They have the test here only in some counties. The county next to mine doesn't do the test, but you need proof that you live there.

Whats the safety test?

 

^ Just a check of the cars safety equipment (lights, brakes, stuff like that.)

 

good job! i live in CA and i've run into this before, usually the cat wants to see a little richer than leaner, although it depends.

too lean = misfires = high HC's