fuel tank selector
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Junior User
Joined: Apr 2019
Posts: 53
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From: Gilbert AZ
fuel tank selector
There are many posts on replacing the fuel tank selector but I have a different issue. For the record my truck is a 77.5 F250. I replaced the fuel selector valve because when I switched from Main to Aux tank the truck stumbled and stall, flip back to main and crank a little it gets fuel. I replaced the valve, fired up the truck on main tank then flipped over auxiliary and the truck runs. I let it idle, check for any leaks and start cleaning up. Truck dies. I switch back to main, this time I set a timer to see how long it runs on aux. Three times it runs for 4:30 and then stalls, no stumbles instant fuel shut off. If the valve wasn't switching over it would run for 20 seconds maybe? But 4 and half minutes is strange. I am only running on main for maybe 20 second then flip over when I timed it. Would it be the switch on the dash? The running for 4-5 minutes has me stumped.
Tuned
Joined: Jan 2017
Posts: 338
Likes: 8
From: North Idaho
Kerby, first of all, the switch on the dash, assuming you are referring to the vertical switch by your heater controls, just puts power to your fuel gauge to read the tank associated. When your engine dies does fuel squirt through your carb when you move the linkage (i.e. are you sure you need to switch back to main) or is your truck indeed starved of fuel?
- IH
- IH
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Junior User
Joined: Apr 2019
Posts: 53
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From: Gilbert AZ
Kerby, first of all, the switch on the dash, assuming you are referring to the vertical switch by your heater controls, just puts power to your fuel gauge to read the tank associated. When your engine dies does fuel squirt through your carb when you move the linkage (i.e. are you sure you need to switch back to main) or is your truck indeed starved of fuel?
- IH
- IH
More Turbo
Joined: Jan 2009
Posts: 547
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There are many posts on replacing the fuel tank selector but I have a different issue. For the record my truck is a 77.5 F250. I replaced the fuel selector valve because when I switched from Main to Aux tank the truck stumbled and stall, flip back to main and crank a little it gets fuel. I replaced the valve, fired up the truck on main tank then flipped over auxiliary and the truck runs. I let it idle, check for any leaks and start cleaning up. Truck dies. I switch back to main, this time I set a timer to see how long it runs on aux. Three times it runs for 4:30 and then stalls, no stumbles instant fuel shut off. If the valve wasn't switching over it would run for 20 seconds maybe? But 4 and half minutes is strange. I am only running on main for maybe 20 second then flip over when I timed it. Would it be the switch on the dash? The running for 4-5 minutes has me stumped.
Dennis
Laughing Gas
Joined: Jan 2018
Posts: 898
Likes: 70
From: Coos Bay
That is the standard replacement valve. The valve defaults to the forward tank, ie. when the truck is off the forward tank is connected. When the truck is on and the selector switch is set to the Aux/Rear, power is applied and the valve moves to connect the rear tank to the fuel system. Block, chock, and remove coil wire from truck, safety first! Remove and plug all fuel lines from the valve. Use a flashlight to see which of the stacked ports the valve is blocking. Use a spray lube to clear remaining fuel from the unit. Put selector valve to the Rear tank and turn ignition to run. Look into ports again to see that valve has moved. Wait the 4 minutes that you timed the fuel starvation during the drive. Check the valve and see if it has relaxed to the default port. If so, check the supplied voltage before turning truck off. If voltage is good, valve is bad. If voltage and valve are operating properly, then you have a clog or no fuel issue between the tank and the valve connection.
Laughing Gas
Joined: Jun 2016
Posts: 855
Likes: 56
From: Des Moines, Washington
I can think of a few reasons why it would run for a few minutes.
A pin hole in the line would let the pump draw in air, reducing the amount fuel actually reaching the carb. On the main tank, the fuel bowl will fill fully. Then when you switch to the aux tank, you are running on borrowed time.
A plugged pick up tube could behave the same.
The wrong gas cap will cause issues with the tank venting, as will a plugged evap line. I’m going to assume a ‘77 has an evap recovery system and therefor should have a non vented cap. My ‘74 does not have an evap system which means it requires a vented cap. Run the truck on the aux tank just short of the point where it stalls then pull the gas cap off. If it goes whoosh or is hard to remove at first, the tank is under vacuum and you’ll need to figure out why.
Michael
A pin hole in the line would let the pump draw in air, reducing the amount fuel actually reaching the carb. On the main tank, the fuel bowl will fill fully. Then when you switch to the aux tank, you are running on borrowed time.
A plugged pick up tube could behave the same.
The wrong gas cap will cause issues with the tank venting, as will a plugged evap line. I’m going to assume a ‘77 has an evap recovery system and therefor should have a non vented cap. My ‘74 does not have an evap system which means it requires a vented cap. Run the truck on the aux tank just short of the point where it stalls then pull the gas cap off. If it goes whoosh or is hard to remove at first, the tank is under vacuum and you’ll need to figure out why.
Michael
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Junior User
Joined: Apr 2019
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From: Gilbert AZ
I ran the truck for 4 mins, I didn't even have to remove the cap, it was hissing when I opened the filler door. now to find out where it is drawing air. I would assume it has to be between the fuel selector valve and the pick up.in the tank.
Laughing Gas
Joined: Jun 2016
Posts: 855
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From: Des Moines, Washington
Based on my assumption that you have an evaporative emissions system, there will be a port on the tank that is plumbed forward to a charcoal canister. What should happen is fuel vapors will travel to the canister, be stored there then either be drawn back to the tank or into the engine to be burned.
I don’t have the system so that’s the extent of my knowledge, I don’t know locations nor routing. I’d would hazard a guess that someone found a loose hose and plugged it for good measure.
Michael
I don’t have the system so that’s the extent of my knowledge, I don’t know locations nor routing. I’d would hazard a guess that someone found a loose hose and plugged it for good measure.
Michael
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Junior User
Joined: Apr 2019
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From: Gilbert AZ
I have been working a lot so the truck has been on the back burner also the 110 degree temps aren't helping me to be motivated either. So being a 77.5 has it's issues, sometimes the parts or diagrams are for a 1977 and sometimes a 1978. After research do have a vented system but that charcoal canister and lines are long gone. By gone I mean it must be plugged (not plugged anymore) close to the top of the tank. I think i need to get a look at the vent coming out of the top of the tank and then replug it. Then I will be back to a non-vented system, no sucking air and my gas caps should work again. I will have some time this Friday to climb under and check everything out.
Laughing Gas
Joined: Jun 2016
Posts: 855
Likes: 56
From: Des Moines, Washington
Based on pictures I found, the vent is slightly forward of top dead center. You may not be able to see it at all without an inspection camera or some fancy work with a mirror. I dropped my tank when I did the filler hose and it wasn't too bad but then it had been empty for 4 or 5 years so it wasn't that heavy. You could switch to a vented cap if you need it running right now and dig into it later when it's cooler. Or you may luck out and find a screw or golf tee wedged into a hose.
Michael
Michael
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Junior User
Joined: Apr 2019
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From: Gilbert AZ
Based on pictures I found, the vent is slightly forward of top dead center. You may not be able to see it at all without an inspection camera or some fancy work with a mirror. I dropped my tank when I did the filler hose and it wasn't too bad but then it had been empty for 4 or 5 years so it wasn't that heavy. You could switch to a vented cap if you need it running right now and dig into it later when it's cooler. Or you may luck out and find a screw or golf tee wedged into a hose.
Michael
Michael