I've heard the 2001-2002 don't have a PEM but I might be wrong. These are the locations I'm aware off on 2003-up The XC90 also has a location inside the left (?) rear wheel well, behind the plastic cover The fuel pumps on these Volvo are unlike what you will find in a Honda or Ford. Volvo ones last ...

Hike over to Advance Auto, get a real fuel pressure gauge, and measure it at the rail. It needs to be up at 50 psi or else Baby won't run.

That will also send you down the right path of troubleshooting.

Your 2001 has a embedded fuel pump relay on the CEM, a PEM, and a modulated fuel pump

Also have a look at the FPS in the same place, if there's one at the right end of the fuel rail. You may also have a external fuel filter, worth servicing it while there