k so the dude i bought the car from told me its obd1..well i just went outside and i could only seen one o2 sensor on the stock header..but i reached my hand beside it and theres another o2 sensor..so then..when i get a header should i have the exhaust shop put 2 bungs in the header just like the pic? http://www.team-integra.net/misc/ima...rs_non_obd.jpg
my ecu is pr3

 

the only cars with two o2 sensors that i know of is the 96-00 civic, and possibly the 96-01 integras but not sure. You only need one o2 bung.

 

the pr3 is obd0, and yes you need the second sensor

 

They make a obd1 pr3 but it is SUPER rare to find that ECU. Came out of a 92 Integra XSi

Yes you need both o2 sensors or you will throw a CEL.

You can check to see if your car is OBD0 or OBD1 by looking at the ECU and matching the plugs up and seeing which matches up.