100 2.5 TDI engine Change !! Help ..

after some advise , pointers or anything you gents can think of ...

my father bought a 100 2.5 TDI with a blown engine , with it was a "replacement". Set to work changing them over ....

now both have the engine code AAT , virtually identical engine ( believe the repalcement came from a 97 A6)

notice one difference in the fly wheel , so we used the orginal . problem is that we can't get any fuel through the pump , even if the pump is primed , NOTHING !!!

the crank shaft has a sensor which is in a different postions , on the 100 its located in the bell housing but on the A6 it's nearer the sump

anybody have any ideas ??

thanks