The ECU can only deliver a limited amount of electrical power. If you put in a big pump or more than one that need a high current draw to reach its rated pressure, the stock ECU might not be able to supply enough juice. For now, on my friend's car with dual Walbros we have relays in place drawing current directly from the battery. I have a background in power electronics so I am designing a circuit that will use the stock fuel pump control to reduce the speed of the pumps for idle and low load situations.
Why would lower voltage cause a motor to overheat and fail?