My girlfriends car is a 1998 Honda Civic EX 2dr coupe, it has a 4-2-1 header on it, a high flow cat and a catback. The problem is that there isn't an O2 sensor hooked up to the cat (universal kind without any O2 sensor wholes), and she has to go for emission testing soon. I know I have to make a whole and weld in a bung, but I dont know where to weld the bung for the O2 sensor. Should it be before the cat (by the two bolt flange)or right after the cat?

 

right after the cat...

 

Should be two O2 sensors, one before the cat and one after.

 

There is one in the header, so the second one that I need to put in should go after the cat?

 

Thats what it sounds like when I read it.

 

Yep, after it.

 

Awesome thanks guys

 

Try to keep it as close to the cat as possible though, you'll get better readings.

 

youre sure its a high flow cat not a test pipe?

 

I pretty sure it is a high flow cat, from what I gathered everything was purchased from ebay from the header to the catback and including the highflow cat.