Can someone explain how the knock sensor circuit works on a 92Z? With the dark blue wire hooked up to the knock sensor, i get 2.39 volts at the wire (by probing the wire at the ECM.) With the knock sensor unhooked i get 4.75 volts at the wire (by probing the ECM.) I know that the 4.75 volts is the reference signal. When i measure the resistance of the knock sensor, i get 3900 Ohms. When the knock sensor detects knock, does it increase or decrease the resistance? I know that resistance increased = current decrease = voltage decrease. So is it a resistance increase(causing a voltage decrease) that triggers the ECM? Thanks in advance.

 

A knock sensor uses a pizoelectric element to generate a very small electrical signal whenever it detects a knock. This analog signal, through the ECM, converts it to a digital signal to control the ignition advance an so forth.

A pizoelectric electric element (I believe that this is a naturally occuring element on Earth, a type of rock - I think) will generate electricity whenever it is hit. This is the same principle that self-starters in ovens or propane torches uses, the type that does not use electricity or pilot lights. When you "start" it, it causes something to hit this element which will create a spark. The harder you hit it, the bigger the spark.

While a "knock" in an engine is by no means as strong as hitting it by a hammer, it is strong enough to create an electrical signal that can be processed (by the ECM) to determine when this condition exists.

[This message has been edited by Stuart Moss (edited July 12, 2001).]