The short story: After a JDM swap, I need to find out what oxygen sensor will work with my 'new' ecu. I have a serial number for the ecu, but I'm not positive what it originally came out of. The longer story: I had a JDM B16a put in my 91 civic. I eventually passed the California inspector's smog test. Now I need to pass smog to renew my registration, but can't. The cat is new, but no matter what oxygen sensor we throw in there, it won't pass smog again. We tried one for the 91 civic, a 94 del sol (what the BAR tested it as), and one that "looked like it should work", so says the mechanic. Sometimes it passes the low-speed test, but flatlines on the higher speed test. The readout looks like it's running crazy rich. Everything else is high, but acceptable. It must be the o2 sensor that's bad, since the cat is the only other smog part on the damn thing. I'm only car-lingo literate up until american muscle cars, btw.