Knock sensor failure?
 

I always had knock reading on my power fc, max was probably around 80-90. One day, it just reads 1 and doesn't change. I've changed my knock sensor and it still doesn't go up. Check wiring too. Any idea what's wrong with it?

the part that was loose fell off?

when i put my car together, i tried the whole box of used knock sensors, and most of them were bad, so if you're using used sensors, you probably got another bad one

The knock sensor wasn't tightened all the way in when I discovered it.