Here is a classic example of a Chrysler 3.6L with a failed valve. In this case no intake valve opening due to a worn / rounded camshaft lobe. No compression on cylinder 6, if you look at the green trace you find a rise in pressure during cylinder 6 intake valve opening. Since the valve does not open pressure increases in intake manifold instead of dropping during the intake stroke

Red Trace: Relative Compression Test

Green Trace: Picoscope WPS500 Pressure Transducer Inserted into intake manifold (nipple that goes to purge valve)

Blue Trace: Ignition Sync (in this case cylinder 2 ignition coil primary)