If the other guy managed to pull up some of the Element Barrels above their alignment Pines and re-installed the not lined up it could have pushed the alignment Pins out of the way or damage the Fuel Injection Pump Housing.
Remove the side cover on the Fuel Injection Pump and you will see at the top of the opening there is a bunch of holes with pins in them. Send a pic of that or if you can tell they are pushed out you will have your answer.

A lot of people don't know the difference between an inch pound torque Wrench and a foot found Torque Wrench. If someone used a foot pound Torque Wrench they could have damaged the Fuel Injection Pump Housing.

The Delivery Valves are 2 mated parts.
If they got mixed up they will not seal correctly.
The Center Valve in the Delivery Valve only mated to one side of the Delivery Valve.
If you insert the Valve into the wrong side it will install without damaging anything but the Valve is not going to seal.

If dirt got into the Fuel Injection Had Lines it would go unfiltered into the Injectors and could bind them up.

In the Pic you see that the Element Barrel alignment Pins are staked in with a Center Punch. If the Pins are pushed outwards it is a sign that the Element Barrel was pulled up and went back in wrong.

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84 300D, 82 Volvo 244Gl Diesel