Regan Brown
Testing a fuel tank selector switch is a common concern for car owners, especially those with dual tanks. The process can be complex and varies depending on the vehicle's make and model. Some common methods include checking voltage, performing fuel pump tests, and inspecting fuel lines and valves. Troubleshooting often involves checking the switch itself, the wiring harness, and the selector valve. While some owners opt for a manual switch, others prefer electric selector valves, which can be tested by checking voltage readings and fuel flow when toggling between tanks.
Characteristics and Values of Testing a Fuel Tank Selector Switch
| Characteristics | Values |
|---|---|
| Testing the rear tank circuit | Briefly apply 12V power to terminals 789 (BR/W) (+) and 786 (R) (-) |
| Testing with a self-powered test lamp or ohmmeter | Connect to terminals 29 (Y/W) and 675 (Y/LB): a good switch will indicate a closed circuit |
| Factory procedure for the reservoir | Performed with all lines disconnected, at air pressures below 5 psi, mimicking fuel line-type connections to avoid damaging the reservoir |
| Fuel pump test connection | Located on the diagnostic link under the hood, with the longest surface of the four-sided plug facing up |
| Fuel pump test procedure | Jump the fuel pump test relay port at the diagnostic link and check for 5-6 oz. of fuel over 5 seconds with the key in the run position |
| Fuel filter requirement | It is recommended to have two fuel filters between the tanks and the selector valve |
| Selector valve testing | Confirm functionality by toggling the switch on the dash to isolate circuits between tanks |
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What You'll Learn
Check for power to the selector switch
To check for power to the selector switch, you can perform a simple test using a test light or a multimeter. This will help determine if the switch is receiving electricity and functioning properly. Here is a step-by-step guide:
- Locate the fuel selector switch: The fuel selector switch is typically located near the fuel tanks and is responsible for switching the fuel supply between the tanks.
- Prepare the test equipment: You can use either a test light or a multimeter for this test. A test light will illuminate if there is power, while a multimeter will provide a more precise measurement of voltage or resistance.
- Connect the test light or multimeter: Touch one probe of the test light or multimeter to a known ground point, and touch the other probe to the connector or terminal of the fuel selector switch. Ensure that the ignition is on so that power is supplied to the switch.
- Observe the results: If the test light illuminates brightly or the multimeter shows a voltage reading, it indicates that power is reaching the selector switch. This suggests that the switch is likely functioning correctly.
- Compare with other circuits: To confirm the results, you can compare the readings with those from other circuits or switches in the vehicle. This will help determine if the issue is specific to the fuel selector switch circuit.
- Inspect the wiring: If the selector switch is not receiving power, carefully inspect the wiring harness for any signs of damage, loose connections, or corrosion. Ensure that the wires are securely connected to the switch and that there is no visible damage to the insulation or connectors.
By following these steps, you can effectively check for power to the fuel tank selector switch and narrow down potential electrical issues in your vehicle.
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Test the rear tank circuit
To test the rear tank circuit, you need to apply 12V power to two of the terminals. These are Terminal 789 (BR/W) (+) and Terminal 786 (R) (-). Once the power is applied, you need to check two other terminals, Terminals 29 (Y/W) and 675 (Y/LB). For this, you will need an Ohmmeter or a self-powered test lamp.
If the switch is functioning properly, connecting the Ohmmeter or self-powered test lamp to Terminals 29 (Y/W) and 675 (Y/LB) should indicate a closed circuit. If it does not, the switch is not functioning properly and may need to be replaced.
It is important to note that there are two circuits in the switch: one for the rear fuel tank and another for the front fuel tank. You need to test both circuits to ensure the switch is functioning properly. The process for testing the front-end circuit is quite similar to the rear-end one but with a few key differences. Firstly, you need to apply 12V power to Terminals 786 (R) (+) and 789 (BR/W) (-). Then, you need to test Terminals 29 (Y/W) and 675 (Y/LB) with an Ohmmeter or self-powered test lamp. A good switch will indicate an open circuit.
Additionally, you should check that the source and return valve transfer between front and rear positions. This will ensure that the switch is functioning properly and allowing fuel to flow between the two tanks as needed.
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Check the fuel pump
Checking the fuel pump is an important step in testing a fuel tank selector switch. Here is a detailed guide on how to do it:
Firstly, eliminate the fuel filter as a potential cause of any issues. Remove the filter from your vehicle and drain any excess fuel. Attach a short rubber hose to the filter inlet and blow through it, noting any resistance. If there is significant resistance, the filter may be clogged with sediment. Inspect the screen for debris and replace the filter if necessary.
Next, check the fuel pump fuse. Refer to your vehicle's owner's manual to locate the fuse box. Identify the fuse associated with the fuel pump and inspect it for signs of failure, such as a break or burn marks. If the fuse is blown, replace it with one of the proper amp rating.
Now, check the voltage at the pump. Consult your vehicle's service manual to determine the correct procedure and location for voltage testing. Perform a drop test using a voltmeter to ensure that the power wire shows the full voltage and the grounding wire is properly grounded. If there is no power reaching the fuel pump, the issue may lie with the fuel pump relay circuit.
If the electrical test does not reveal any problems, it is likely that your fuel pump requires replacement. However, for further confirmation, you can perform a pressure test. If your car has a pressure test valve, with the car turned off, press the valve to see if fuel squirts out. Additionally, you can try the following: turn the car on for a few seconds, then turn it off and try pressing the valve again. Alternatively, remove the fuel pump fuse, crank the engine, disconnect the fuel filter, attach a hose to the tank side, turn the car on, and observe if fuel comes out.
By following these steps, you can comprehensively check the fuel pump as part of testing and troubleshooting a fuel tank selector switch.
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Inspect fuel lines and fittings
Inspecting the fuel lines and fittings is an essential step in maintaining the health of your boat or car's fuel system. Here are the detailed steps to inspect the fuel lines and fittings:
First, it is crucial to disconnect the battery to prevent any accidental sparks that could ignite petrol or petrol vapours. Ensure that you are working in a well-ventilated area and that there are no naked lights or cigarettes nearby. Use a torch instead of an inspection lamp to avoid the risk of fire.
Next, start by examining the fuel lines for any signs of damage, including cracks, splits, or corrosion. Look for any wet areas around the joints, as petrol may run along the pipe before dripping. Bend flexible pipes between your fingers to feel for any cracks or splits. Push on clips and metal joints to test their security. If you notice any damage or leaks, it is important to replace the affected parts as soon as possible.
After inspecting the fuel lines, focus on the fittings. Check if the fittings are securely attached and free from any damage or corrosion. Look for any signs of fuel leaks around the fittings. If you notice any issues with the fittings, refer to the manufacturer's guidelines or seek professional assistance for replacement or repair.
Additionally, pay attention to the anti-siphon valve, which is typically located in the outlet fitting from the tank to the engine. The anti-siphon valve prevents fuel from flowing into the bilge in case of a fuel line failure. If you experience fuel restrictions to the engine, do not remove the check valve from the anti-siphon fitting. Instead, replace it with a quality anti-siphon valve to maintain safety.
Finally, when inspecting the fuel lines and fittings, it is important to consider the age of the components. Manufacturers typically recommend a lifespan of 10 years for gasoline hoses. However, it is advisable to inspect the fuel lines annually and replace them if there are any concerns. Newer fuel hoses often have an inner liner to prevent deterioration from alcohol-extended fuels. Ensure that any replacements comply with EPA standards and use appropriate clamps and fittings.
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Refer to the service manual for testing procedures
The service manual should also outline the correct testing procedures for the selector valve. This will include information on the terminals, which are: Pin 1: Not used, Pin 2: 789 (BR/W), Pin 3: 786 (R), Pin 4: 673 (DB/Y), Pin 5: 29 (Y/W), and Pin 6: 675 (Y/LB). To test the rear tank circuit, you will need to briefly apply 12V power to terminals 789 (BR/W) (+) and 786 (R) (-). Then, connect a self-powered test lamp or Ohmmeter to terminals 29 (Y/W) and 675 (Y/LB). A good switch will indicate a closed circuit.
The service manual may also provide information on testing the inertia switch cable. This involves checking the power supply of the switch. An inadequate power supply to any selector wire will disable the inertia switch. To do this, you will need to pull out the selector switch from the dash by prying the dashboard compartments around the switch with a screwdriver. Then, check the power of each terminal. The power should be 12V in each terminal. If every terminal has 12V power, then the switch is functioning correctly.
Additionally, the service manual may recommend testing the terminals of the fuel selector switch. There are two circuits in the switch, one for the rear fuel tank and one for the front fuel tank. Both circuits should be tested using an Ohmmeter to check the voltage of the front and rear-end circuits.
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Frequently asked questions
If your vehicle is not switching between fuel tanks, this could be due to a faulty selector switch. Check if the gauge works when switching between tanks. If the gauge works but the selector isn't switching, this indicates a problem with the selector switch.
You can test the switch by checking the voltage at the selector valve. Disconnect the hot wire from the valve and measure the voltage. If you have 12V when disconnected and 4.5V when connected to the main tank, this indicates the selector valve is working correctly.
A faulty fuel tank selector switch may cause the vehicle to not start, as fuel pressure may be lost. You may also experience no flow to the high-pressure pump when switching to the auxiliary tank.
If you suspect a faulty fuel tank selector switch, you can either replace it with a new one or try to find a used one from a junkyard. You can also refer to the service manual for your vehicle to perform a component testing procedure on the selector valve.
Yes, it is important to follow the factory procedure for testing the fuel system. Disconnect all lines and ensure air pressures are below 5 psi to avoid damaging the reservoir. Also, be cautious of any dangling wires that may be connected to the voltage regulator.
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