I'm trying to give you all the reasons I can think of to NOT mess with
the injection pump itself. The IP MUST be fed fuel for its "pumping
action" relates only to its 2,000 psi impulses to the injectors, not to
its own fuel supply. That's done by the engine's fuel pump down at the
primer pump's base.

Did you purge the air from the fuel system after the new filters were
mounted? Pump hand primer pump until no air bubbles are visible in the
lines?

The injection pump can be repaired by a Bosch center - phone book /
internet "diesel injection service." They do trucks and construction but
may point you to someone who can help you if they can't. Know where
you're going to take it before plunging into the job.

If you absolutely have to remove the IP it's essential to FIRST set the
motor to a known rotation point so the IP's timing is not lost. The IP's
drive gear has an intentionally missing tooth and a mark cut into the
collar behind the drive gear. Aligning the IP's gear with the collar is
24 degrees BTDC on the crankshaft so you need to turn the motor by hand
- right hand rotation - (pull and push on the drive belts) so 24 degrees
BTDC on the harmonic balancer is achieved - on the compression stroke of
#1 cylinder (look at #1's cam lobes through the oil filler opening they
should BOTH be pointing UPward).

The engine manual shows the two oil lines from the oil filter to the oil
cooler being removed AFTER the filter is opened to allow the lube oil to
drain back into the motor (and not onto the floor). The oil filter
housing is then removed so the IP can be pulled out. A new gasket is
essential as are clean surfaces or it will leak afterward.

Before loosening the IP's three mounting bolts note their position and
scribe onto the IP and the motor some marks to use later to achieve the
same IP position and thus the same injection timing as current - without
having to time the injection.

The IP is lubricated by engine oil (and has a small oil pipe to it.
Prior to its reinstallation you ought to fill 1/2 pt of lube oil into it
(there's a fill plug near the top rear, above and slightly aft of its
lube oil pipe)

Getting the picture of why NOT to remove the IP?

If it were my car I'd (i) be absolutely assured that the IP was getting
lots of fuel and if the problem persisted  (ii) remove the IP's high
pressure lines (but not the hold down clamps) and from each well remove
the spring and plunger and crank the motor knowing that diesel fuel will
be spilled - the idea being to flush fuel through the IP. I'd remove the
IP only after all else failed.

I hope this helps get your car back on the road.