They symptoms of valve in the Fuel Supply lift pump not seating well are if the vehicle sits over night it takes a lot of cranking to get it started.

If that happens let it sit unused over night again and before you start pumping a lot on the hand primer. If it starts OK that is an indication your Fuel supply Lift Pump needs to be rebuilt.
Depending on which pump you have kits were between $17-$37. Bosch kits are more then the generic kits.

However, a small air leak on the suction side could also cause the same symptom.

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84 300D, 82 Volvo 244Gl Diesel