You need the wiring diagram TP3907202 Its a 205 page PDF file with schematics
and diagrams to locate components. Whats your email ?, I'll send it to you.

Page 64 of the PDF file (Which shows page 59 of the Volvo document ) is the
locator for the fuel system components. It shows the main fuse block with the fuses and two rows of relays. The page before has the schematic.

Even more plain is on PDF page 12 (Volvo page 5) where all of the relays are identified.

You'll see that the relays are numbered in order starting in the center of the car towards the windshield and progressing towards the drivers side

101/102 is the first a twin size rectangular relay
103 is a small square relay and
104 is half of a twin size relay ending that row

the front row closest to the fuses is 3 small relays 105, 106, 107, and 108 is part of the twin relay 104

101-102 103 104
|
105 106 107 108

Does that make sense to you? It's easier to look at the Volvo book!

Are you sure that you have spark? Your issue is a puzzle since you sometimes don't hear the fuel pump, but have fuel at the rail. If that's the case
then the pump is working and maybe the injector relay by the radiator is bad.

What exact relay socket did you try a jumper? There's 3 relays.
If you hear the pump, AND have fuel at the rail, and it doesn't start- try jumping the relay 2/32 Pins 3 and 4, This is the relay above the radiator.

according to the schematic
pin 3 of the socket = #87 on the relay (Green wire) and
pin 4 on the socket = #30 of the relay (One of the red wires)
The key is to get +12V on the green wire that is the +12 for the injectors.
While you're at it, confirm that the intake manifold ground is OK/tight etc.
If that is off, you might get the weird hosing that you're suffering.

Hopefully you don't have water in the fuel.

Bill