You will know for sure when you swap the lift/fuel supply pump.
The lift/fuel supply pump has a spring loaded piston and a rod that rides on the IP camshaft (while the lift pump is off get a light and mirror and take a at the cam the pin rides on).

The pin pushes on the piston against the spring and pumps the fuel out.

The spring pushes the piston back sucking in the fuel. Things that can happen-the spring can break and the push pin some times breaks also. The piston can stick also.
If the problems above happened the hand primer would still work because it is a separate pump.



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84 300D, 82 Volvo 244Gl Diesel