Oil pressure vs lifter pump up

There are exceptions to every rule but valve springs are the main component in the valve float department. What happens with weak valve springs and hydraulic lifters is when the valves start to float it makes a clearance in the valve train then the hydraulic lifters being their purpose is to take up clearance, will try to make up this clearance. Now the lifter, until it bleeds down a little will hold your valve open. This is why some people blame the lifter when really it was doing it's job and the valve springs are the ones that needs to be replaced.

Chuck