Smog Q? Maybe for bdcardinal?

If everything else is functioning right, a different x pipe will not make your car run rich. Also here in Winston Salem, they no longer use a sniffer test for obdII cars. Just the obdII test, so if you aren't throwing any codes, you should pass.

It's because the cats are further downstream. Something to do with the exhaust cooling off too soon; before it goes through the cats. The O2 sensors only have so much of a range they can allow before having to throw the MIL, which in turn will adjust the car's air/fuel ratio. There's a much more technical explanation of it all out there somewhere; I just know that one of the reasons was because of the cats being further down the system. Another reason was some of the catted midpipes come with high-flow cats, which sometimes flow too much. Or, there's the one I saw where the 'high-flow' cats turned out to simply be little baby glasspacks.