FRPM delete: Return fuel system with bosch 044 external pump - Forums at Modded Mustangs
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post #1 of 2 Old June 14th, 2019, 09:44 PM Thread Starter
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FRPM delete: Return fuel system with bosch 044 external pump

I have an 03 4.6 system in my 61 F100. I used all wiring harness and FPDM from the car. The issue Im running into is I used the pump drive wire from the FPDM and ground to the Bosch 044. So after studying a bit I found out that the 044 is not getting constant 12V it needs. I have been reading that I can leave the FPDM in place and use the 12v FPDM switched power (from Fuel Pump Relay) to power a new relay and basically bypass the FPDM to drive the pump but leave it in place so I dont throw codes. So teh FPDM power will go to 86 on the new relay. 85 is new ground to frame. 30 is the direct input from the battery (fused and constant) and 87 goes to drive the fuel pump. Is this correct? I am using an LS swap filter and 58 PSI pressure regulator unit. pic of truck and LS swap regulator/return shown
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post #2 of 2 Old June 15th, 2019, 12:31 PM
Troy McClure
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Yep that arrangement sounds correct for your typical relay. 85/86 is your trigger and ground (direction really not that important), 30 is your power and 87 is your switched item, in this case a fuel pump.

Nice build and looks like a pretty clean installation.

58psi is pretty high for your typical modular engine, but if the injectors are sized appropriately and it's tuned correctly it shouldn't be an issue. 39psi is the normal pressure with the returnless systems, and jumps to 51psi at high temperatures to prevent vapor lock. I know a lot of guys go to 51 with return systems since it doesn't have the flexibility to switch pressures, and the increased heat in the fuel making it more prone to vapor lock.
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