Chevy & GMC Vans

Hello, I have an '87 Astro with a 5 speed which seems to run pretty well. I say "seems" because the knock sensor does not seem to be working or the ECM is not responding to it. I have no error codes and I have tried to diagnose the problem by tapping on the block near the sensor and listening for an RPM drop but the RPM remains constant. I have also tried disconnecting the ESC module but still no change in the RPM. I considered that the RPM change was so subtle that maybe I couldn't discern it over the sound of the engine and so I connected a tachometer which also showed no change. I was wondering how to test the knock sensor to see if it is working. I also purchased another ECM and it does the same thing, it seems to run great but the knock sensor doesn't seem to respond.

You really need to put a timing light on it to test the knock sensor.

to expand on that....
put a timing light on it and rap on the block or a head with something metal, if the knock sensor is working you will see the timing retard, as in the opposite of advance (no jokes you jokers).
As this has to be done with the engine running, two people are best for this. reaching over a running serpentine belt is a particularly great way to loose a few fingers.
Remove the doghouse, do the rapping from the backside of the engine.

Thank you for the advice. I did connect a timing light and with a friend's help I was able to see...well...something...the timing mark seemed to move ever so slightly when the block was tapped repeatedly. I'm not sure how much movement I was supposed to see. Honestly, maybe my eyes were just playing tricks on me because I so desperately wanted to see some kind of evidence to suggest that the knock sensor was indeed working. Well, On account that I think I saw something and I'm not getting any codes from the E.C.M. I'll consider it working.