Rajan Wilcox
If you're experiencing issues with your 1987 F150's fuel tank switch, you're not alone. Many F150 owners have reported similar problems, often related to the fuel gauge not working or the truck running off the front tank regardless of the tank selector switch position. While some issues may be caused by faulty wiring or fuses, others could be due to problems with the fuel pump or selector valve. To diagnose and resolve these issues, it's important to refer to official wiring schematics and consult experts for guidance.
| Characteristics | Values |
|---|---|
| Vehicle | 1987 F150 4x4 |
| Cab type | Standard |
| Bed size | 6 1/2' |
| Tank configuration | Dual |
| Problem | Fuel gauge reads empty; truck runs off the front tank regardless of tank selector switch position |
| Possible causes | Faulty switch, wiring issue, blocked valve, faulty fuel pump |
| Solution | Check fuses, test voltage, clean or replace wires, replace fuel pump if necessary |
| Resources | Wiring diagrams for similar models (e.g., 1986 F150), multimeter, test light |
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What You'll Learn
Troubleshooting a faulty fuel gauge
Step 1: Check the Fuel Gauge Itself
Before assuming the worst, it's essential to ensure that the issue lies within the fuel gauge. Disconnect the dash fuel tank selector switch and turn the key. If the fuel gauge reads above full, it indicates that the gauge is likely functioning correctly. This simple test can save you time and effort by ruling out the gauge as the source of the problem.
Step 2: Inspect Wiring and Connections
One of the most common causes of fuel gauge malfunctions is faulty wiring or connections. Check the wires on the tank, especially the one reading full, to ensure there are no signs of damage, corrosion, or loose connections. Additionally, inspect the brass float on the sender for the tank reading empty, as this can impact the accuracy of the fuel level reading.
Step 3: Evaluate the Fuel Level Sending Unit
The fuel level sending unit plays a crucial role in measuring the fuel level in the tank. If the sending unit is faulty, it can lead to inaccurate or no readings on the fuel gauge. Check the resistance of the sending unit using a diagnostic multimeter. The sending unit should measure approximately 55 ohms when empty and 155 ohms when full. If the readings are off, it's likely that the sending unit needs to be replaced.
Step 4: Consider the Voltage Regulator
Another potential culprit of fuel gauge issues is a faulty voltage regulator on the instrument panel. The sending unit operates using a 5V pulse from the voltage regulator, so any malfunction in the regulator can impact the sending unit's performance. Use a diagnostic multimeter to test the voltage and, if necessary, replace the voltage regulator.
Step 5: Test the Fuel Pumps
In some cases, the problem may lie with the fuel pumps themselves. Ensure that both the front and rear tank fuel pumps are operational by listening for their activation when the tank selector switch is turned on. If one of the pumps is not functioning, it could be causing the fuel gauge to read inaccurately.
Step 6: Consult a Professional
If you've exhausted the above troubleshooting steps and the issue persists, it may be time to consult a professional mechanic or Ford truck specialist. They will have the expertise and equipment to diagnose and resolve more complex problems related to your F150's fuel gauge.
Remember to exercise caution and refer to reliable resources or seek expert advice if you're unsure about any procedures.
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Testing the tank selector switch
The next step is to test the tank selector switch. This can be done by using a multimeter to check voltages. One user reported that they got 10.7V to ground through the switch at all the right places and 1.7-1.8V back from the tank going to the gauge. It is important to note that when working in the fuel system, a test light should be used instead of a meter to avoid incorrect readings.
Additionally, it is recommended to check the wiring for any signs of tampering or splicing, as this can affect the functionality of the selector switch. The power wires to the pumps are red for one and brown with a white stripe for the other.
In some cases, the issue may lie with the selector valve rather than the switch. Cleaning or replacing the selector valve has been suggested as a solution by some users.
It is also worth noting that the fuel gauge may be functioning correctly, as disconnecting the dash fuel tank selector switch and turning the key resulted in the fuel gauge reading above full for some users.
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Checking the voltage on the tank fuel pump wiring
Firstly, it is important to use a test light instead of a meter when checking for voltage in the fuel system. A meter does not load the circuit, which can lead to inaccurate readings. Connect the test light to the Cab body or the NEG post of the battery for a ground, rather than the frame or bed, as they may not be grounded properly.
Now, turn the key to the 'on' position. At this point, you should check the voltage coming out of the fuel pump wiring at the tank. A normal reading would be around 12 volts. If the voltage is significantly lower, it could indicate a problem with the fuel pump or a high resistance in the circuit.
Next, you can try testing the voltage at different points in the circuit. For example, check the voltage at the red wire on the inside of the cab, as well as the voltage coming from the PCM power relay. Additionally, check for voltage at the fuel tank selector valve while someone else switches the selector.
It is also important to inspect the wiring for any signs of damage or corrosion. Spliced wires or corroded connector pins can affect voltage readings and fuel pump performance.
Finally, if you have access to a wiring diagram for a similar model, such as the 1986 F150, you can compare voltage readings at various points in the circuit to identify any discrepancies.
By following these steps and checking the voltage on the tank fuel pump wiring, you can gain valuable insights into the health of your Ford F150's fuel system and identify any potential issues.
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Identifying the correct tank selector switch
To identify the correct tank selector switch for your 1987 F150, you will need to determine the specific model of your truck. Since your truck has been recently painted and has no decals or emblems, you may not be able to identify the exact model by visual inspection. However, you can refer to the vehicle identification number (VIN) to ensure you are ordering the correct parts.
The fuel tank selector switch is an essential component of the fuel system in your F150, allowing you to switch between the dual tanks. It controls the pump and sending unit in both tanks and feeds the fuel gauge.
When ordering parts for your F150, it is crucial to provide the Vehicle Identification Number (VIN) or the specific part number you need. This will ensure you receive the correct fuel tank selector switch for your truck. You can refer to Ford parts websites or authorised dealers to find the correct switch for your specific model.
Additionally, you can try visiting a wrecking yard to find a replacement cluster cover, which may come with a spare selector switch. However, when replacing the switch, ensure that you pay attention to the specifications and dimensions to avoid compatibility issues.
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Understanding the wiring diagram for the fuel system
The fuel system wiring diagram for the 1986 F150 can be found in the official wiring schematics and the EVTM's. However, these schematics are spread across multiple pages, making it difficult to understand the entire fuel system at a glance. This has prompted some people to create their own single-page diagrams, which can be found online.
When working with the fuel system, it is important to use a test light rather than a meter, as meters can give incorrect readings. By using a test light, you can more accurately diagnose any issues with the fuel system wiring.
The fuel system in the 87 F150 is a dual-tank system, with one tank in the front and one in the rear. The fuel tank selector switch allows you to choose between the two tanks, but there have been reports of issues with this switch. Some people have reported that their trucks are always running off the front tank, regardless of the position of the switch. Others have reported problems with the fuel gauge, with the gauge reading empty or not working at all.
These issues can often be attributed to problems with the wiring or the fuel pump. It is important to check the voltages at the switch and the fuel pump wiring to ensure they are within the correct range. Additionally, the fuel level sending unit may be the cause of the fuel gauge issues, as this is a common problem with these trucks.
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Frequently asked questions
The problem could be with the wiring to the pumps, or a bad switch. Check the wiring and replace the switch if necessary.
Check the fuses and the wires going to the sending unit on the frame rail. Ensure that the wires are connected properly and are not cut off.
Check the fuses and relays. If they are fine, then you may need to replace the fuel pump.
Check for power to the selector switch and the frame fuel pump. You may also need to test the relay. If the frame fuel pump is not working, you may need to replace it.
