IMHO, the pre-prime feature is a bandaid for weak lift pumps (w/lazy check valves) and/or mask airleaks that often occur when the vehicle is parked for extended periods, overnight for example.
'Air-ports' are driven by atmospheric pressure, which is constantly assaulting the fuel supply system, relentlessly searching out any system breaches regardless if the system is in use or not..
Lots of physics but in a nutshell.. When not in use, the fuel supply system should remain sealed in order to maintain a slight positive pressure. However with time and use, the liftpumps one way check valves become worn and lazy and may not remain sealed as it should do when new..
As such, the liftpump will allow the fuel to drain back to the fuel tank but only if atmosphere (14psi) breach's the inoperative fuel system and displaces (replaces) the fuel thats otherwise would remain 'suspended' above the fuel tanks lowest fuel level.
Atmosphere is always trying to equalize the fuel's level to the lowest point.
When the fuel system is operating at minimal fuel pressures, the 'suction' line is subjected to an extremely low pressure zone created by the liftpump pressurizing the fuel supply system. Atmosphere, always trying to equalize the negitive pressure in the suction line pushes the fuel from the tank towards the liftpump. So in a sense, atmosphere pressurizes our fuel tanks during normal operations..
IF theres any weaknesses in the suction line, atmosphere will expose them creating an air leak.. Sometimes air leaks are only exposed during max fuel flow, when fuel pressure is at its lowest, many capable of opening and closing like a 'zipper'... Suction line is the worst for hiding 'zippers'..
IF theres any fuel restrictions (ex- clogged fuel strainer or FFM element, or kinked or crushed fuel line) causing fuel pressure to drop below 3psi at any time, especially during high fuel flow demands, it exposes the entire system to atmospheric assaults as well as entrained air too...
The DS4 IP is a serious binge drinker. Most often it sips the fuel but its capable of demanding instantaneous big gulps of fuel when engine suddenly loads up while your already cruising 75mph for ex.. Its during these MAX FUEL FLOW demands with minimal fuel pressure that atmospheric assaults are greatest..