ok i made my own test pipe but i didnt have a 18mm nut and i couldnt find one anywhere so i just zip tied the o2 sensor up under the car doing this wont hert or mess up anything will it and if it dose what will it do thanks

 

I'm no expert, but I would think that getting that sensor wet or otherwise subjecting it to whatever debris flys around the undercarriage might not be so good. I'd say wrap it up in a plastic bag or something, but I'm not sure if your sensor placement is next to a heat source which might melt the plastic and cause damage.

I don't think the sensor will read anything different to throw a CEL, but I'd seriously look into protecting that sensor. It's not cheap.

 

I'm all for making my own stuff. This is one of those cases, though, where a little extra cash goes a long way. If you were able to weld the flanges onto the ends of the pipe, and if you were able to drill a hole in the side of the pipe well enough to get the sensor to fit then you should be able to weld a nut on there to hold the sensor. I'm thinking you did some serious MacGuyvering on this one.
I'd avoid plastic anything. The test pipe gets hot enough that I can touch it for about three seconds when I'm wearing my welding gloves before I think my hand is going to melt away.

My guess is that this project maybe cost you $20 and quite a few headaches. You should really check out
http://www.roadracemotorsports.com/
http://www.buschurracing.com/cgi-bin....cgi?18X376545 (it's 2.5" piping, a little bigger than some would recommend, but it's only $50)

You are really almost better off not even attaching the O2 sensor than risk having it fall out and hang or otherwise get damaged.
Sorry if I sound heavyhanded on this, but I'd feel even worse if I didn't say anything and you wrecked a fairly costly part (I can't get one at any of my parts stores, but I've heard the sensor runs $200 or more )

 

i did a great job on the test pipe (as far as welding and things go theres no leaks) and the reason i didnt weld a nut on is cuz i coulnt fined one that big anywhere really all im woried about is. dose the o2 sensor tell the motor anythin or is it just there so people dont take the cat off if having it off the car (not in the pipe) is going to do is set off the cel light then im not going to take it back off and put a nut on there so i can put the o2 sensor on i dont care if the cel light is on or not

ps: i did put a bag around the o2 sensor and taped it up so nuthing can get on it and its zip tied way off to the side so nuthing burns or melts it