2-speed fuel pump?
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From: Central NYS
2-speed fuel pump?
I'm working on a 1999 F-450 with the V-10.
I'm trying to get my head wrapped around the wiring for the fuel pump (aft tank).
According to the wiring diagram there is a fuel pump relay in the relay block that supplys power to the fuel pump. I'm okay with that.
But there is also a "fuel pump speed relay" on the ground side of the fuel pump circuit. If I'm reading the diagram correctly, when the PCM energizes the "speed relay", the fuel pump ground is sent through a resistor to ground and when the PCM de-energizes the "Speed relay" the fuel pump ground bypasses the resistor and goes straight to ground.
Is this in effect a two speed fuel pump?
And does anyone know what the PCM's logic is?
Like when is the fuel pump put into high speed and when does it go into low speed?
Thanks for any light you can shed on this.......................Jim
I'm trying to get my head wrapped around the wiring for the fuel pump (aft tank).
According to the wiring diagram there is a fuel pump relay in the relay block that supplys power to the fuel pump. I'm okay with that.
But there is also a "fuel pump speed relay" on the ground side of the fuel pump circuit. If I'm reading the diagram correctly, when the PCM energizes the "speed relay", the fuel pump ground is sent through a resistor to ground and when the PCM de-energizes the "Speed relay" the fuel pump ground bypasses the resistor and goes straight to ground.
Is this in effect a two speed fuel pump?
And does anyone know what the PCM's logic is?
Like when is the fuel pump put into high speed and when does it go into low speed?
Thanks for any light you can shed on this.......................Jim
Thread Starter
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Logistics Pro
Joined: Jan 2001
Posts: 3,740
Likes: 37
From: Central NYS
Next I wanna dead head the fuel pressure regulator to see if its leaking pressure back to the tank
And would really like to know what conditions cause the PCM to activate/deactivate the speed relay and how much that resistor will lower the fuel pump voltage and when before springing for a new pump.
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