Knock Sensor


I was not happy with the way most knock sensor indicators worked. They really don't give much information. So I decided to do something different and wire the knock sensor up so I could hear it over the car's stereo. The idea behind it is simple the knock sensor is a piezoelectric device that generates a small electrical current when it is vibrated. Pretty much the same as a microphone but able to withstand temperatures much better than a standard mic.

For this I used a standard AC Delco knock sensor and installed it on the block. The metro block has a sensor_thumbnail small boss sticking out between the #1 and #2 cylinders on the back of the motor. It is right beside the alternator.The Delco sensor could be installed in the normal position but it would interfere with the alternator so I did it slightly different. I took the top bolt out of the alternator and took the top bolt off the plastic shield for the alternator so I could tilt it away from the motor. I then used a small drill bit and drilled a hole through the boss at an angle so the sensor would stick up at an angle and stay away from the alternator. I only drilled through half of the boss. When I hit the factory hole I stopped. I then went to a larger size bit and drilled it out the correct size and tapped it for the threads on the knock sensor. After that it was a simple matter to screw the sensor in and hook a wire up to it. I used some old speaker wire I had laying around. I grounded the second wire to a nearby bolt. I ran the wire into the car through the firewall and attached it to a 1/8 stereo jack. I can now plug in my tape adapter to that jack and insert it into my tape player to listen for knock.


The knock sound is pretty easy to recognize once you figure out what is what. First thing I did when I had it hooked up and working was  to retard the timing as far as it could go on the car. I twisted the distributor as far as it would go then snugged the top bolt to hold it in place. I took the car for a drive listening to the sounds the sensor picks up. Unless your car has some real problems none of those sounds are engine knock. After doing that for a minute I turned the distributor all the way advanced as far as it would turn. I then started out driving and immediately started hearing the sharp clicking sound of engine knock. I got the car up to about 45MPH before I had enough of that. I pulled over the side of the road and turned the distributor to about the middle and drove it accelerating back up to 60mph while listening for knock. I didn't hear any so I advanced it a bit and tried again. I got knock so I went to the middle of the last two tries and got no knock. I turned it up a tiny bit more and more till I got knock then backed it down to where I didn't have any knock. I then drove it home trying all kinds of different throttle loads and gears listening for knock. Once I was home I put the timing light on and checked my timing. I was at 8 degrees advanced. This was a pretty good indication that setting the timing by the stereo worked real well.