After you are done with your Car for the day loosen your Fuel Fill Cap enough to relieve any Vacuum and leave the Cap loose over night. In the morning before you tighten the Fuel Fill Cap if the Car will Start normal. If it does you have something causing a Vacuum in your Fuel tank like a restricted Fuel Tank Vent.

For the pump itself.
Is there any chance that the small diameter shaft on the Valve is sticking in the Bore it rides in?
Remove Cap that is in the Bottom of the Lift Pump that holds the Valve and spring. Remove the Valve and spring and take the Valve and stick it back into the bore in the Lower Cap. gently move it up and down and rotate it a little and see if it is sticking any where.
If it seems to be sticking there may be a metal burr in the bore or on the edge of the bore. If there is remove it.
If the Valve itself is too tight take some fine Wet/Dry sand paper and sand it down some to reduce the Diameter of the shaft and see if that will free it up.

Compare the New Spring with the Old Spring and see if they are the same length. Use which ever has the longer length.

If you still have the old Valves you could compare the old to new Valve and see if there is any physical differences in them.

Look to see if the Head of the Old Valve is smaller in diameter than the new Valve.

__________________
84 300D, 82 Volvo 244Gl Diesel