the ECU is the electronic control module & removing it's electrical plug in eliminates any possibility of an "open" frying any electronic components during our testing. consistant readings pretty much are we are wanting to have & they will vary from ~120-170 psi roughly depending on the CR & the cam & you would want them to be the same within maybe ~10% or so & I am not positive on that % figure. But do post the readings. We are hoping to NOT have 2 adjacent cyls that are WAY lower than the others which would indicate a blown head gasket between the two offending cyls. I would get one that screws in to the cyl with a detachable hose rather than cheap one with a rubber tip that you have to hold to the plug hole while someone cranks the eng & they are not expensive.