Pontiac: knock sensor/computer, knock sensor, faulty sensor

Question
Hello
Car: 88 cadi/cimarron 2.8, no jokes please, i know i use the word cadi losely...heh

Prob: poor running.took car to shop, machanic says; >computer tells car its knocking! but its not!
so i replace the computer and the problem with advancing the timeing too much goes away!

But slowly returns over a week to the same problem?
Could this be a short in the knock sensor curcit or a faulty sensor? the mech said he tested the sensor and found no prob? hmm

Can i test the curcit by disconeting it? is this curcit normally open or closed?

any help would be great!

Thanks, Mike  

Answer
The knock sensor has a piezo crystal inside that when vibrated(like from an engine knock) will produce voltage. The more severe the knock or ping, the more voltage the sensore produces. This voltage signal is what tell the ECM how much it should RETARD the timing. If after retarding the timing, the knock sensor is still producing voltage, the ECM "should" turn the check engine light on to let you know that there is a problem. Notice I said "should". It doesn't always work the way it should.
You can check the resistance of the sensor but I'm not sure of the specs off hand. The problem that you are having, with the problem coming back slowly, is because the ECM stores knock sensor signal info so that it can try to control future spark knock before it happens. So when you replace the ECM, you are basically only resetting the memory for the knock sensor info. You could try to unplug the knock sensor and see what happens, but you also need to make sure that you dont have an engine knock or spark knock problem first. If spark knock is a problem, you can try a better grade of gas or you might have a problem with the EGR system that is causing it to ping(spark knock).