I just swapped a gsr motor into a 94 civic. Now theirs no wiring on the harness for the knock sensor and the ecu is recognizing it and throwing a knock sensor fault code. I know that when you throw a fault code it cuts your ecu back into safe mode resulting in a loss of power and terrible gas mileage. Does that same thing still apply with something as small as a knock sensor??

 

The knock sensor is not an electrical load, it actually produces it's own voltage. Your ECU is looking for a variable voltage from the sensor. So in short yes.

 

you should run a wire to the ecu. its a pain to get the pins in, but it can be done. try to get a harness that plugs into the ecu from a junkyard, then take it apart till you can get a couple of pins out, then splice the new wire to the pin.