From what I understand, these fuel pump relays use a pulse width modulated signal. So, low voltage isnt really fesable since its constantly changing (well, on and off that is). What I am thinking is something internally in the relay is going nutty, just like every other relay Volvo has used.

When I go down there this weekend, I am going to drive the wheels off of it till I get it to stall, then im going to go nuts and work as fast as I can to see if I can get it diagnosed before it feels like it wants to start again.