Magnum EFI Return or Returnless? & Vacuum Regulator Question

robcuda said

I have been reading about this and I believe my donor vehicle used voltage to the pump to address any issues of regulation. Now that I'm not using the stock fuel pump I think I will have to use vacuum to the regulator. Maybe this will be a more crude approach to regulate vs. the ECM doing it on the donor car.

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Your 1997 donor truck did not use voltage to regulate pressure. It's a returnless system with a regulator built into the fuel pump assembly in the fuel tank. Running an aftermarket regulator mounted near the fuel rail on the engine allows you to set it up exactly like the 92-94 factory regulator. Functionally, it's the same.
The vacuum line on the factory setup is so it has normal pressure under no load, then slightly higher pressure under heavy load, like full throttle acceleration. Not sure if your aftermarket regulator is vacuum referenced or boost referenced, but the instructions for it should clarify that.