Fuel pump problems kangoo 2006 multix

my car keeps cutting out, so i replaced the fuel pump with a 2.5 generic pump..only to be told that i need a 3.5...so i bought a 3.8, however still have intermittent problems.. i have now been told the reason that this is so: the original fuel pump has an on board regulator, is this true? I went to the bosch agents and were told that there is no such fuel pump in their catalogue book..so i am stymied at the moment