Knock Sensor used as a Switch



Hi Guys,

:unsure:: Does anyone know if a tuneable aftermarket knock sensor could be used as a switch to activate a water injection system?

I'm thinking of a normally aspirated engine that has fairly high compression. I think the use of a 50/50 mix of alky and water would be more efficient than retarding the timing.

A knock sensor is nothing more than a piezo microphone. It is listening for noise corresponding to a knock. When it hears such noise it tells the ECU. Depending on rpm, load, etc., the ECU will then adjust an output to reduce advance. It will continue to reduce advance until the microphone no longer hears the knock. Then it advances the ignition again until knock is heard.

So no, it's not a switch and can't be used like one. You could design a circuit that could listen for knock and then activate a relay. You could make the sensitivity adjustable. That shouldn't be too hard for some of the rocket scientists here. :unsure:
Certainly easy enough to do. Ask me after I retire in 40+ years, I may be able to sketch something up then :roll: :cry: :oops:

Actually, a knock sensor, being a piezo-electric GENERATOR, actually makes a small voltage spike when it "hears" a sound corresponding to it's range. From what I have seen and heard with these, if you hook up an led to the output, and tap the block with a hammer, the led will flash. This output could then be hooked to a transistor to amplify the signal, and from there to a relay. So, in that sense, yes, it can be used as a switch, but just go get a GM one-wire sensor, to save the headaches of using a Ford 3-wire.