Okay its kinda a long story but here it is. I have a 93 civic vx (0BD1) with a 98 b18c1 (OBD2), and a P72 ecu (OBD1). For some reason, I was running extremely rich and my ecu threw a code #1. Since I know this motor was once turboed for a short period of time, I figured the O2 sensors and cat were shot. So I replaced the cat with an aftermarket one (OEM spec) and I just replaced the O2 sensor with a bosch universal. I only found one O2 sensor on the cat and none on the exhaust manifold so my question/ problem is this. . . after all this, my ecu just threw another code #1 ! Is that correct that I only have one O2 sensor before the cat? Was the person that did my swapp supposed to use the exhaust manifold O2 sensor or does it even matter? Has anyone else had this problem converting an OBD2 motor to OBD1? I need to pass smog at the state reff and this shit sucks. Somebody please help.