Compression test

The engine has to be cranking to do a compression test, but all that will do is tell you what the compression is. You can do a cylinder leakage test that doesn't require cranking the engine. That will tell you where the most compression is leaking out, intake valve, exhaust valve, piston rings, or head gasket. You'll need compressed air. Many auto parts stores that rent or borrow tools will have the tester.