In engine diagnostics, what is the main purpose of performing a 'wet' compression test after obtaining a low reading during a standard 'dry' compression test?

1. To clean the soot out of the combustion chamber valves
2. To determine if the compression loss is due to worn piston rings or leaking valves
3. To lubricate the dry spark plug threads before reinstallation
4. To test the strength of the cylinder head bolts under pressure