Wheres my buzzz gone

Ok 1996 Disco 300tdi auto (EDC) so now down to injector pump when i used to turn the key the injector pump used to buzz or maybe that black box on top of the injector pump used to buzz but now its stopped working and my Disco cant rev and lacks power on occasions it will start to buzz again and my disco runs fine so my question is 1 what the feck does THAT BLACK BOX DO and 2 more importantly can it be replaced it looks like its held in by 4 torx screws i have tried Land Rovers and the young lad didnt no a lot about old Disco (who does) also the independents couldnt really help and as for the injection pump guys £££££s. but before all that if i can replace that black box thing it may just work. Thanks guys your help so far has been great. Louis

Come on someone must know what that black box is on top of the injector pump is or does

i shall ask my matey tomorrow for you and find out what it is and let you know

That would be great. its started to do my head in

could this be down to an ecu fault cutting the injection pump in and out