I'd try using an o2 sensor from a teg, not a dx. Not sure though. b18a1 should only have 1 o2 sensor. on the 90-91 it was on the header, the 92-93 was just before the cat. That's just where they put it stock though, it doesn't matter where you put it if you get an aftermarket header as long as it's one or the other. You do not need two though. Unless for some crazy reason you converted your car to obd1-2 which i know nothing about.