we have a 91 us market made in japan crx here with a engine swap from a 91 JDM crx. we have tracked down and repaired many wiring problems. the car now needs the O2 sensors hooked up to make it run in closed loop. there are 2 O2 sensors one is simply called O2 sensor and the other was labeled dual O2 sensor. I need to know where this second O2 sensor lives. before the cat?after the cat? if before where in the manifold will both live. the oem manifold is not on the car either it has a DC sports header.
some other information:
engine. B16a
ecu# 37820-pr3-j00
410-209052
date on the ecu. 91-7-09

simple to the point answers are welcome.
thanks in advance
Shaun

 

the primary o2 sensor goes in the header/manifold
the secondary o2 sensor goes before the cat.

 

they both go on the header... primary catches cyl 1 and 3 secondary catches 2 and 4