If the fuel pump is bad there will be no pressure coming from the pump even if the mechanic were to hook direct power to the unit. A low pressure system may be caused by a blockage in the system or even low voltage from the alternator. A major cause of fuel issues is the FPR or fuel pressure regulator which is a unit that controls the flow of fuel to the injectors. If this unit were to function incorrectly it would cause low fuel pressure at the injectors and the car would have issues running and starting.
Cracks in the fuel lines and bad seals in meeting points can cause fuel leaks that can not only cause low pressure in the fuel system but can also be dangerous due to the highly flammable nature of the fuel. If there is a fuel leak in the system it could be caused by old dry rotted line or cracks in the system from impacts of rocks and other debris from the road. If the issue is tracked back to the fuel pump it may be a much smaller issue than the whole pump. If the wiring has a short and cannot get the proper voltage to the pump then the electric motor cannot function at full power and will not provide the correct pressure. Sometimes the voltage sent from the alternator is just too low and cannot power the pump unit enough. In the end it is better to check out the cause of the issue then just throwing in new parts and hoping it fixes the issue.
