If you have at least 1/2 Tank of Fuel you can swap the Positions of the Fuel Outlet Hose (the Cigar Hose) and the Fuel Inlet Hose where they attach at the Fender Well. That will bypass the fuel Tank Screen and draw Fuel from a higher position in the Fuel Tank (do that for testing only as it also means you would run out of Fuel early).

If the situation improves your Fuel Tank Screen is restricted.

You could also replace the 2 sections of Fuel Inlet Hose with 5/16" ID regular Fuel Hose you can get at the Auto Parts Store as it is also rated for Diesel Fuel.

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84 300D, 82 Volvo 244Gl Diesel