Fuel system clarification
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Fuel system clarification
Hello everyone I am about to embark on my first big project on my 1985 ford f-250 7.5L. I am basically going to be replacing the whole fuel system. I Will be replacing both tanks the side mount and the rear one behind the axle. the fuel tank selector switch as well as the whole fuel pump assembly( it is the electric in the tank not the mechanical). I am new to working on vehicles and this is my first "Project Truck" so I have a few question about these older trucks that may seem obvious to you guys so bare with me lol. This is my first vehicle with dull tanks. I do not have the owners manual but am I right in assuming that the rear behind the axle and front side mount are both 19 gallon tanks? Also can I use the same in tank fuel pump and sending unit in both tanks. one does not require a different pump than the other, right? also is there anything else I should know or any other parts I should be replacing when I embark on this project. I appreciate any tips or tricks you guy can give me!
FTE Legend
Joined: Nov 2015
Posts: 30,828
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From: Angier, NC
If the truck has a long bed (8 feet) then yes both tanks are 19 gallon tanks.
Only the short bed side tank was the smaller 16 gallon tank.
As for the sending units / pumps well .....
I am going to say the electric pump its self are going to be the same but the sending units would be different between them.
So in short the sending units are different and if they come with the pumps then then good .
Look up new sending units to see if"
1 they come with pumps or not.
2 if they are different for the side & rear tank and my guess they are.
If you come across any rubber hose replace it now, who knows how old it is.
If you replace the fuel filler hoses there has been issues with how long the rubber part is. I forget who has the right ones? Fuel neck guy or something like that??
Also the inner plastic vent hose is fun to deal with. It must be put back in place just right or you will have issues when you go to fill the tanks.
Oh it is best to remove the bed being you are dealing with both tanks and th rest of the fuel system.
Dave ----
Only the short bed side tank was the smaller 16 gallon tank.
As for the sending units / pumps well .....
I am going to say the electric pump its self are going to be the same but the sending units would be different between them.
So in short the sending units are different and if they come with the pumps then then good .
Look up new sending units to see if"
1 they come with pumps or not.
2 if they are different for the side & rear tank and my guess they are.
If you come across any rubber hose replace it now, who knows how old it is.
If you replace the fuel filler hoses there has been issues with how long the rubber part is. I forget who has the right ones? Fuel neck guy or something like that??
Also the inner plastic vent hose is fun to deal with. It must be put back in place just right or you will have issues when you go to fill the tanks.
Oh it is best to remove the bed being you are dealing with both tanks and th rest of the fuel system.
Dave ----
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From: Virginia
Your fuel system is more complex than the similar trucks that year. Unless it was fuel injected, it did not come with electric pumps except the trucks like yours with the hot fuel handling package. Your system has more electrical components in it, and these have more of a tendency to fail as the truck gets older.
Your pumps get power directly from the starter solenoid/relay on the pass side fender when cranking. But after it starts, the pumps get power through a fuel pump relay which is activated by a oil pressure switch. And after that, the power goes through a "inertia" or crash switch before it goes to the pumps. And then of course in the mix you have the selector switch. As you can see, you have more and more places for failure as the system gets some age on it.
Your pumps get power directly from the starter solenoid/relay on the pass side fender when cranking. But after it starts, the pumps get power through a fuel pump relay which is activated by a oil pressure switch. And after that, the power goes through a "inertia" or crash switch before it goes to the pumps. And then of course in the mix you have the selector switch. As you can see, you have more and more places for failure as the system gets some age on it.
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