Rap on the block with a hammer and see if timing retards? I really don't know what RPM range it functions in. Rumor has it that at some point some parts stores had testers for them. The fact that these can be bypassed leads me to believe it's creating a voltage output when knock is detected. So if you can identify the output pin and find a non-destructive way to break in (extra terminal and a depin tool?), the hammer test should show an output. Sorry, never done it.