A compression test will only give you a general idea of engine health
It WILL NOT help you to understand if there is gunk buildup in the engine
It WILL NOT tell you if you have a specific issue with your valves or rings
It WILL give you an idea of whether you have good compression or not.
A compression tester will give you an idea of whether you cylinder is maintaining the necessary pressure or compression in order to operate properly. If you compression reading are below the manufacturer specifications then you will need to further troubleshoot using a leak down tester to discover if it is one of the following that is your issue.
The problems you can discover through a leak down test are the following.
Bad head gasket
Leaking exhaust valve
Leaking intake valve
Bad rings
Here is a link to a good article regarding how to use a leak down tester.
