'94 coupe that's already using the D3 spot? Hmm, I remember helping a guy with a VX hatch and I think the factory O2 sensor (VX's have a weird multiwire O2) used D3 and he reused to the wire to power his knock sensor and it worked but I didn't know of any coupe's with that setup. I would try resetting the ECU by simply disconnecting the battery (you gotta reset your radio presets but eh, so what). I also don't want to sound rude, but I would recheck the location that you added the wire to at the ECU. I don't think their should be a wire already in the D3 location on a coupe. I'm attaching a little graphic I made after I did my swap with the pinout locations, you can try checking against that. When I first did my swap, I just twisted the wires, shoved them through the back of the ECU plug and connect it back and it worked. I later got some real ECU pins, soldered and heatshrinked the wires to them and added them to the harness but we wired it into D5 (I couldn't remember the pin location) and had a check engine light. I haven't really heard too many things about knock sensors failing so I doubt it's the sensor itself. Hopefully this will fix you up.