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On FP managed systems, if you hot wire the pump it produces ~80# which is where the over pressure bypass relief dumps the excess back in the tank. I hot wired one to drive it to the shop to get a new fuel pump put in. '02 and later Bulls use this system. The PCM can trim the fuel trims to let it run. My pump was bad so it did not run with the module but would when hot wired.
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If the pump is on full power all the time then it needs a regulator (vacuum controlled) and return line, or pump will burn up.
 

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On return systems, there is a pressure relief/regulator on the fuel rail. It lets excess fuel return to the tank. On the '01 one year only system the relief is in the fuel filter and you have a return from the filter to the tank. Both use battery volts to the pump. On the power regulated system, the FPDM regulates "effective voltage" to the pump and it runs at a volts that gives the pressure the fuel pressure sensor on the fuel rail tells the FPDM to do. ('02 and later) This system uses less power from the system. Only enough power to meet the need. That system has a pressure relief inside the tank set to 80#. It is a safety system and should never be needed in normal driving. In not driving situation, heat buildup can cause expansion in the fuel lines and that will let that small amount to release back to the tank.
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