I have been experiencing engine knock recently. first it knocks upon cold start. If i immediately place the car in gear and drop the rpms slightly the knock immediately stops. This has been going on for some time now. WHat is more concerning is that now after highway use the car knocks when accellerating away from a stop. It never knocks at speeds in excess of 15mph. I am seeing acceptable fuel milage at 20-25mpg highway. I would think that the knock sensor would retard the timing if it sensed detination but it seems to not be functioning. I have set the mechanical timing back to 8 degrees before top dead center to compensate for increased compression caused by a 17 thousanths head mill job. Where is the knock sensor located and can it be tested?