Leak tests are usually used to determine the cause of a low compression reading on a standard compression test.

Perform a compression test. Start the engine, allow to get to operating temperature. While engine is running, remove the fuel pump fuse and allow to die from fuel starvation. Turn off ignition.
Remove all spark plugs. One cylinder at a time, crank engine over, throttle open, allow up to 10 compression strokes or until the gauge stops moving up.

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2003 4.6, esotril blue, over 215,000KM. Every previous owner failed to keep up the vehicle maintenance. Restoration project.