The basic place to start is to change the Fuel Filters and make sure you are getting Fuel to the Fuel Injection Pump. (It only takes one load of contaminated Fuel to stop up even a new Filter.)

If you have more than 1/2 Tank of Fuel I believe the swapping of the Fuel Inlet and Outlet Hose positions that can be done on the 123s where the Tubings going back to the Fuel Tank are will also work on your SD.
That bypasses the Fuel Tank Screen and draws Fuel from a higher position in the Fuel Tank (only for testing because you would also run out of Fuel sooner than your Gauge indicates if you leave it connected like that).

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84 300D, 82 Volvo 244Gl Diesel