Take a spark plug and knock all the porcelin out of it. Braze a male air coupler to it. In succession roll each cyl. to TDC, attach the coupler to an air hose and regulate it down to 50 psi or so, more will flop the engine over, and listen 1. air horn (intake valve) 2. Tailpipe (ex, valve) 3, oil fill (rings) and 4. look for a stream of bubbles in the radiator neck (head gasket, valve seat, block etc.) While this is not as scientific as the special tool, it will allow fair comparison and often locate the problem. Good luck.
One other point... on that tool install a pressure guage. It's nice to see how much pressure is lost over a given amount of time. If you have a 6 cylinder engine you take 6 reading and compare them to each other. If ALL the cylinder readings are about the same and there is no leak detected, your engine's probably OK.
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