I have a b16a1 in a 89 Civic hatch and it has 2 O2 sensors, or it came that way when i got it back For the Shop after the install, Is both o2 sensors needed?
and what do both of them do?
Also I just installed a Max Rev turbo kit and im only runing one of them today
and it runs fine untill i get to 9lbs of boost then i get a code 3 check engine code
i know that this code is for the map sensor how do i cure this problem?

 

you need the 2.

you can splice them into 1 but hmmm. You could get a program for your ecu that removes the use of them.

if you're keeping your stock computer you need them both for appropriate functions.

one is for 2 cylinders and the other is for the other 2

 

mine has 2 O2 too, I though they only use one in JDM land