Running Rough and Stalling when Gas Level is at Half Tank 2008 Volvo XC90 3.2cyl

[lilduke]

Hello,

The car is running smoothly, but starting last Monday(03/17/2025), it runs rough and stalls once the gas level reaches half a tank. A New Volvo fuel pump was placed in the car in February.
Do you have a suggestion for what could be the culprit of the problem? (Fuel pump pressure not being strong enough; one of the motors in the fuel pump being burnt out; sending unit no longer working)

[Vova585]

Due to the AWD system, engineers had to be creative and made fuel tank in a way so driveshaft to the rear wheels can pass through. So it is basically 2 chambers connected with narrow area on top. I'm 1 chamber you have fuel pump(main pump) on the other chamber there is either a small(priming pump, helper pump, I am not sure of terminology) that simply pumps fuel from one side into the side of the main fuel pump. Sometimes there can be systems that perform this transfer work via utilizing work of the main pump(possibly venturi effect, once again It is not that relevant). I would concentrate on sending unit diagnosis and make sure the pump is working correctly, hose between sides is not cracked, plastic connectors not broken, pick up screen on sending pump/unit is not dirty .
First find what exact system and parts you have using vin code. Can go to local dealer and ask them to print you parts diagram of your system and you will know what parts are there. Next look at video from PHAD(pine hollow auto diagnostic) about "volvo from hell" it will be about 05xc90 so you will get and idea. He is opening tank in that video and explains how it works(credit to Ivan from PHAD). It is 5parts video, so will be worth your while to watch it.

[abscate]

In this forum user shockwave wrote up a great tale of how a dealer incorrectly installed his fuel pump in his XC90 and kinked the supply line, leading to an intermittent complete engine shutdown. It went a week typically before failing, just enough time for him to declare the care safe and give it to partner with child. Fun.

viewtopic.php?t=83957&hilit=Shockwave

This is an epic tale of careful troubleshooting mentality that you have to follow and learn. It is not googleable.