I was under the understanding that all plugs should be in, since you are also plugging the one cylinder you are testing. That way all cylinders are plugged. This is what I was told from a co-worker who builds race engines as well as daily drivers. Also, cranking revolutions should be the same on all cylinders (5-6 revs) even if it is still building pressure. Or, if it is still building pressure, go back to the other tested cylinders to test at that higher number of revs (7-8?).
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