im not real sure but isnt a test pipe just a straight thru pipe in place of the cat? also if so how will that affect my car? will my check engine light come on?

 

Yes, and yes (wrt CEL).

 

Ummmm actually a lot of us have been running testpipes with no CEL. Basically what happens is if you completely remove the 02 sensor or just shove it back into the floor, then it will have a CEL.

But most of the people that covered the 02 in foil and zip tied it to the shift linkage have not had a CEL.

So yes it will affect your car, it will smell like fumes no matter where you are. The degree depends on mileage. And no if you do it right will not have a CEL.