Well first off don't run the engine with the quick connects disconnected. That is an open center system, which means that the fluid has a open/low resistance pathway all the way thru the valves and back to the sump with everything connected. High volume flow, low pressure, untill a valve control is actuated and fluid is sent to a cylinder(lower flow, higher pressure, work is performed). Hydraulic fluid must always flow in these systems. By separating the QC's, you are most likley deadheading the pump. This is very bad for the pump, seals and hoses as there is no flow and extreme pressure, and no safety to vent the excess pressure that builds immediatly when the flow stops. Pump cases crack, seals and hoses blow, pump shafts twist and break, ect...
It sounds, from your description like your pump is loosing it's prime or sucking air. Check all the suction line fittings between reservoir and pump. It is very easy to suck air in a leak on the suction line instead of sucking oil along the line. You could also have a clogged suction line strainer, usually locatd where the suction line gets it's oil from the sump. You could also be low on hydraulic fluid in the reservoir. If you find no problem with the suction line fittings, strainer or fluid level, it is possible that you have a damaged seal or cracked case on the pump that is admitting air on the pump body or around it's drive shaft.
