Needing to know where the knock sensor is located and how would I replace it

This is in reference to a '93 Lumina Euro I bought new and is a single owner car. Although there are no knocking noises, the check engine code indicates a faulty knock sensor and there is a definite loss of power even though the engine runs and idles smoothly. The exhaust smells like the engine is running very rich. All this just came up I quess when the sensor went bad. Yes the milage actually is 311,000 with no major repairs and it doesn't burn oil. Whoaa! All else is ok.