"David L. Johnson" wrote: (clip) I guess the pump is somehow defective,
with some blockage in the presta side of the head.
^^^^^^^^^^^^^^
If you operate the pump with the Presta setting, but not connected to a
valve, does it register any pressure on the gauge? Compare this to the
Shraeder setting. Is there a difference? On the Presta setting can you
compress air, so you have a gauge reading that does not bleed off? It could
be that there is a scrap of rubber in the valve that is blocking air flow.