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I worked in the engine field for 30 years, I am not aware of any test that determines lifter health by bleeding them down engine off. Personally I think that was a waste of time. If you think you have loose lifters causing noise grab a rubber hammer. Place the wood end on the rocker arm with engine running, press on the rubber end putting pressure down on the push rod side of the rocker arm, this will quiet a noisy lifter.. This forces it to adjust, hold it a minute and release, I am thinking about 25-40 lbs of pressure not a light push. It should adjust again right away and run smooth. If it does not react properly you found the bad lifter or the location of a loose lifter. The cause could be a bad lifter or a cam going flat. Engine off you might find a collapsed lifter just by checking each push rod but to do this you would need to check each cylinder while that cylinder was at TDC on the compression stroke to be sure both lifters should be loose. All 16 lifters at TDC compression stroke should have very similar play if not identical play. Hydraulic lifters adjust all the time in normal use, you are looking for one that no longer adjusts in normal use or is sticky. Get a mechanics stethoscope or take about 4' of 5/8 heater hose and hold it to your ear. Search the running engine with your scope or hose trying to find the location of your sound. It very well may be your damper or even a loose bolt somewhere in that area hitting on something. The rhythm of the sound should give a clue if it is a piston, rocker arm or rod bearing. The damper would have a faster rhythm. Hope you find it and it is minor.
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