Please help, X5 Stalled at low fuel, need your opinion.

[Pongsak X5]

My 01 X5 3.0i 55 Kmiles 'd stalled for 3 rd time. As i post previously i thought it came from fuel filter (no obc errors) and i'd changed it already for 3 months ago, everything 's fine then(but i never left the fuel below 30 l.).
Yesterday night when i drove at 70 mph and fuel remained 20 l , the engine suddenly shaked and gear changed abnormally (come and go) for 10 seconds then it stalled.
I remembered that all the stalled occurred when the fuel 's around 20 l. After I filled gas for only 10 l. The engine can start normally (fortunately , it stalled next to the gas station) and no problems with the engine or transmission afterward.
The question is what's the cause of the problem? Why the gas can't below the 20 l. level in only this X5?
Please help, I need you opinion.
Thanks a lot.

[chris_barry]

Havent looked into the X5 tank, but most EFI systems have two pumps. A low pressure pump that picks up fuel and tops up a surge tank. When full the surge tank overflows back into the main tank. Then they have an immersed high pressure pump which supplies fuel to the engine. If the low pressure pump has failed then fuel can only slosh into the surge tank so the high pressure pump can run dry.

General layout is a barrel shaped pump assembly that is immersed in the fuel tank. This has the high pressure pump inside it, and a lower pressure on the side of it.

Sometimes the low pressure pumps have a plastic mesh bag than hangs down from it and reaches the bottom of the tank. I've seen these filter bags drop off inside the tank so the low pressure pump cannot reach the last inch of fuel.

Good luck.