compression gauge peak and hold valve?
 

I tore my compression gauge apart to build a leak down tester, but never put it back together. Now it won't do peak and hold when cranking, and I suspect it was something I did to it when tearing it apart. Anybody know if it is the bleed valve type that sits in the neck? or is it something else?

you probably took out the check valve that holds the pressure constant or the release is jambed.