The first thing that has to be established is what OBD is this engine and ECU? If it is in fact an OBD-0 B16 then the 2 O2 sensors originally came in the primarys of the factory manifold, not the down pipe, or before and after the cat. Before and after the cat is for OBD2 cars. Your best bet is to convert it to 1 O2 sensor. If I am not mistaken HASport's website has a section that tells you how to do it right.