Peter,
Depends upon what is wrong with the pump. I had injector pump on 1970 220D fail to feed to #4 injector. Rear camshaft ball bearing had come apart allowing the camshaft to drop so that #4 plunger would not operate. A $7.50 ball bearing fixed the problem. This problem occurred at about 200,000 miles---this pump now has a little over 720,000 miles, having survived two short block replacements. When working on injector pump and removing parts a clean work surface is essential. And as has been pointed out, some parts you don't mess with---like the two nuts that hold each holding flange at element assembly (not present on the 220D pumps).

__________________
K. Weimer
300SD (1)
300D (5) [Plus 1 parts]
300SEL 4.5 (2)
280SE (4)
280 (2)
250 (1)
250SE (1)
240D (7) [Plus 1 parts]
220D (11) [Plus 3 parts]
200D (2) [Plus 1 parts]
180c (with sunroof)

1995 Nissan UD1800 rollback
"If I can't fix it, it don't get fixed"