i got it done yesterday and i faild my emision where to high. this creep said that it was because my o2 sen is on only one piston so i have to move it lower where it can read them all i have a d15 y8 with dc headers could it be my cat back is durty

 

It would be nice if you could post the results but if the O2 sensor is only reading one cylinder and that cylinder is a little lean, then the ECU will drive all 4 cylinders richer, not just that one so yes, you need a header or pipe that allows the O2 sensor to read all four cylinders, you either had high HC or high CO or you were a gross polluter.

Is that tester a test only station or can they do repairs too, if he is test only, he is not allowed to give you troubleshooting help, but in this case he is correct about one thing, it may not completely fix your car though, but is the first place to start.

 

Your header might have another O2 bung by the collector and extend the wire. That is the way my DC is on my D16A6.

The stock exhaust 02 only senses off of two cylinders so I will let you make the call. I don't think that is your problem. Unless that cylinder is not doing to well.

Post the numbers we will try and help