I have a 1990 honda accord automatic i wanna put a performance header catback and exhust on it but the available parts comes with 2 o2 sensors opening and not one and the car only have one would it be safe to still install

 

Yes, all you need is to plug the second bung with an M18 X 1.5mm plug.

 

Most will come with a plug.

 

I have noticed that with some of the cheaper offshore models it is 50/50 whether or not they throw in a plug. Easy enough to pick one up at your local parts store. M18x1.5 oil plug will work!