How do you perform a leak down test?

To perform a leak down test, first, ensure the engine is at top dead center (TDC) on the compression stroke for the cylinder being tested. Disconnect the spark plug and connect a leak down tester to the spark plug hole, applying compressed air to the cylinder. Observe the pressure gauge; a significant drop indicates leaks, and you can listen for escaping air at various points (like the intake, exhaust, or crankcase) to identify the source of the leak. Finally, repeat the process for each cylinder for comprehensive results.