I have a friend who has replaced his mechanical pump on an IO-360 twice due to low pressure.  It normally ran around 23 psi and was replaced because it sporadically dropped to about 7 psi. We are considering the unique apparent failure of a second pump after only 35 hours. 

 

Larry,

 

Sporadic drops in pressure are often due to air in the line.  Boost pumps have been occasionally tagged as the perpetrator of the leak that introduces air, even though the boost pump restores the pressure (24-28 psi, anything above about 14 psi works marginally).  Another, of course, is a hot line that vaporizes the fuel - any changes since things were working fine?  Hmmmmmm, where is the pressure sensor located in the system.  Any possible slightly loose fuel line connections?  Is the airplane named Christine?

 

Hard to believe that two pimps failed in a row.  Hmmmm, the i is next to the u.

 

Otherwise, just bad luck with two bad pumps??