Katerina Swanson
The 1984 Ford F150 is a truck with dual fuel tanks. The dual tank system allows drivers to switch between the front and rear tanks while driving, ensuring a constant fuel supply. However, some owners have reported issues with their dual tank systems, such as the rear tank starving the engine or the truck running only on the rear tank. In some cases, the previous owner may have modified the fuel system to run only on the rear tank. To restore the dual tank function, owners may need to replace both tanks, sending units, and the tank selector valve. Additionally, it is important to regularly check the rear tank line and clear any clogs to ensure the dual tank system works efficiently.
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What You'll Learn
Fuel tank selector switch
The 1984 F150 has dual fuel tanks, with one tank at the front and the other at the rear. The fuel tank selector switch is located in the cab and can be toggled to switch between the two tanks.
The fuel tank selector switch is usually found to the right of the heater/AC controls. However, in some trucks, the switch is located underneath on the frame rail. The switch may be labelled "Left & Right" instead of "Front & Rear".
If you are having trouble locating the switch, try following the wires from the tank switch valve.
If you want to get back to a dual tank system, you will likely need to replace both tanks, sending units, and the tank selector valve. The tank selector valve is available with 3 or 6 ports and may require a toggle switch and pigtail connector for installation.
It is important to note that the fuel reservoir has a failure mode where it will use fuel from one tank and return it to the other. This is purely mechanical, with no wires, and relies on pressure from the in-tank pumps to move the reservoir valve. Therefore, the in-tank pumps must be working for the system to work on a fuel-injected engine.
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Troubleshooting fuel gauge
Troubleshooting a fuel gauge issue on a 1984 F150 can be a tricky process, but there are some methods you can try to diagnose and potentially fix the problem.
Firstly, it's important to understand the fuel system setup on this vehicle. The 1984 F150 features a dual-tank system with a fuel tank selector switch, allowing the driver to choose between the front and rear tanks. The selector switch is located in the cab, and the fuel gauge should reflect the level of the selected tank.
If your fuel gauge is reading empty or not functioning correctly, there are a few potential causes and solutions to consider:
Check the Sending Unit and Wiring:
- The sending unit, located inside the fuel tank, may be faulty. Try testing it by connecting a known good sending unit to the wiring. If the gauge responds accordingly, the original sending unit is likely defective and needs replacement.
- Inspect the wiring harness connected to the sending unit. Ensure that all connections are secure and free of corrosion or damage.
Verify Fuel Levels and Tank Selector Switch:
- Check the fuel levels in both the front and rear tanks. It is possible that the previous owner modified the system to run only on the rear tank, as mentioned in your research.
- Verify that the tank selector switch is functioning correctly. Toggle the switch between the front and rear positions and observe the fuel gauge's response. If the gauge does not reflect the correct tank levels, the selector switch or its wiring may be faulty.
Inspect the Fuel Gauge Itself:
- Remove the right-side dash cover to access the fuel gauge. Inspect the gauge for any visible signs of damage or corrosion.
- If the gauge appears intact, consider testing it with a known working sending unit to determine if the issue lies within the gauge itself.
Check the Fuel Pump:
- In-tank fuel pumps play a critical role in both fuel delivery and cooling. If the pump is not submerged in fuel, it can overheat and become damaged.
- Measure the fuel pressure at the test port on the engine. Low or zero pressure indicates a pump issue.
- Check for power and ground at the pump connector while cranking the engine. If power and ground are present but the pump is not running, it likely needs to be replaced.
Please note that these are general troubleshooting steps, and the specific process may vary depending on your vehicle's unique configuration. If you are uncomfortable performing these tasks or unsure about the procedures, it is always best to consult a qualified mechanic.
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Replacing the selector valve
If you want to restore a dual-tank system in your 1984 F150, you will likely need to replace both tanks, sending units, and the tank selector valve.
Firstly, it is important to identify the motor and fuel system in your vehicle. If it is a 300 six with a 3-port switching valve, it is an easy system to fix. The 3-port valve, with 2 inputs and 1 output to the carburettor, defaults to the rear tank when there is no power to the valve. You can easily swap the rear tank hose to the front inlet valve and the front hose to the rear inlet.
If your selector valve is leaking internally, it can cause issues with fuel pressure. You should replace the front pump and, if the problem persists, replace the selector valve.
You may also need to replace the selector valve if your engine is running but the rear tank is defective and not running. In this case, you should check both pumps with a stethoscope to see if they are on. If the pumps are not working, check if they are receiving power. If they are receiving power but not running, you have a bad pump and will need to replace it.
If you are replacing the selector valve with an electronic version, such as the Wells FSV2K or the Standard Motor Products FV5K, you will need to determine if their electronics compensate for the lack of a reservoir or if you need to incorporate a reservoir into the fuel line.
It is worth noting that the original '86-'89 dual tank system is considered one of Ford's worst designs, and you may want to consider redesigning your truck's fuel lines or swapping all the fuel lines and tanks to the '90-04 system.
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Fuel tank rust issues
The 1984 Ford F150 with dual fuel tanks is a popular model, but some owners have experienced issues with fuel tank rust. Here are some tips to address this problem:
It is not uncommon for the fuel tanks in the 1984 F150 to develop rust, especially in the rear metal tank. This can be caused by dirt and moisture buildup between the skid plate and the tank. The tanks are not painted, which can exacerbate the issue. One temporary solution is to apply epoxy to any rusted areas, but this may not be a long-lasting fix.
Inspection and Cleaning
If you suspect rust or sediment in your fuel tank, it is recommended to inspect and clean the tank and fuel pump. Dropping the tank for inspection may be necessary, and it is often easiest to do this by removing the bed of the truck. Cleaning the tank can help remove any rust or sediment buildup, and it is also advised to inspect the fuel pump pickup screen.
Fuel Filter and Sending Unit
The fuel filter plays a critical role in preventing rust and sediment from entering the sending unit and fuel lines. If the filter is damaged, rust and sediment can pass through and cause issues such as erratic stalling and failure to start. Therefore, it is essential to regularly inspect and replace the fuel filter as needed. Additionally, the sending unit itself can rust, especially on the outside, so it may need to be replaced if heavily corroded.
Dual Tank System
If you are running a dual tank system, both tanks, sending units, and the tank selector valve may need to be replaced. However, some owners opt for a single tank system, especially with the availability of ethanol fuel, unless frequently driving in remote areas where fuel is not readily available.
Fuel Injection
For fuel-injected engines, the system relies on pressure from the in-tank pumps to move the reservoir valve. Therefore, the in-tank pumps must be functional for the dual-tank system to work correctly.
Remember to consult a qualified mechanic if you are unsure about any maintenance or repair procedures.
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Fuel line hose replacement
To use dual fuel tanks in a 1984 Ford F150, the fuel tank selector switch must be set to the desired tank (front or rear). The truck will run on the rear tank if the switch is set to the front tank and vice versa. It is purely mechanical, with no wires, and the pressure from the in-tank pumps moves the reservoir valve.
Now, here is a step-by-step guide on how to replace a fuel line hose in a vehicle:
Step 1: Drive the vehicle around the block and monitor the fuel level and engine light. If the engine light comes on, there may be an issue with the fuel system or an electrical problem.
Step 2: Place a small drip pan under the fuel hose to catch any spills.
Step 3: Remove the hose from the attaching fuel line, fuel pump, or carburetor using a fuel hose quick disconnect tool. Be sure to also remove the hose clamp that holds the fuel hose in place.
Step 4: Clean the surface where the fuel hose attaches with a lint-free cloth.
Step 5: Remove the fuel hose from the supply side of the fuel pump and the fuel steel line from the vehicle.
Step 6: Place a transmission jack or similar jack under the fuel tank and remove the fuel tank straps and mounting bolts to the fuel filler neck.
Step 7: Lower the fuel tank enough to access and remove the plastic or rubber fuel hose from the fuel pump. You may need to disconnect other fuel lines to reach the hose you are replacing.
Step 8: Install the new fuel hose onto the fuel pump, fuel line, or carburetor. Ensure the hose is not too long or too short, and there are no kinks or bends that could obstruct fuel flow.
Step 9: Tighten the new hose clamps to secure the hose in place. Do not reuse old hose clamps as they may not hold properly and cause leaks.
Step 10: Reconnect the negative terminal on the car's battery and pressurize the fuel system by returning the fuel pump fuse to the fuse box.
Step 11: Start the engine and allow a few seconds for the fuel to flow through the system. If everything is connected correctly, the engine should run normally.
Note: Always work in a well-ventilated area when replacing fuel hoses, and have a fire extinguisher nearby. It is recommended to replace all rubber or flex hoses on the supply, return, and vapor lines if only one hose is damaged.
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Frequently asked questions
You can switch between your dual fuel tanks by using a fuel tank selector switch, which is usually located in the cab of the truck. If you are having trouble getting your truck to run on the front tank, it may be because the previous owner modified the fuel system to run only on the rear tank.
If your truck is only running on the rear tank, you may need to replace the tank selector valve or the fuel lines. Check the rear tank line to see if it is clear, and try opening the gas cap to see if it is vapor locked. If it is not vapor locked, try blowing air back through the line to clear the pickup in the tank.
You need a 3-port manual fuel tank selector valve. The original valve is likely controlled by a single wire and has no plug-in. Make sure to purchase a brass valve to prevent leaks.
