New to the forum, long time Volvo owner.

I recently replaced the fuel filter with a 122827 - Mahle - Fuel Filter - P80 850 S70 V70 C70 - 30671182 from IPD.

in the mornings when I start the car, or it has been sitting longer than 2-4 hours, I have to prime the system by turning to ignition multiple times. I can hear the fuel pressuring in the system from the back of the car forwards

edit: 1999 Volvo v70 wagon 2wd non turbo

 

Fuel pressure may be leaking down due to a bad fuel pump check valve or the pressure regulator on the other end. Verify leak down with a fuel pressure gauge. Isn't there a rubber hose on the exit of the fuel pressure regulator - you could easily block the pressure regulator exit to verify if it was the fuel pump loosing the pressure.