check valve in compression gauge is stuck open.
Compression gauge has a check valve that allows pressure in but not out.
Because engine compression is temporary, you would need to watch the gauge while cranking and couldn't get an accurate reading, so these gauges have a check valve, well should have and need to have a check valve.
Usually there is a button you press to release pressure before testing the next cylinder, thats the check valve.
Yes, 170's would be expected from 2.3l