Checking Fuel Pressure On Your Subaru: A Step-By-Step Guide

Checking the fuel pressure of your car is an essential step in fuel pump testing. It can help diagnose potential issues and ensure proper fuel delivery to the engine. To check the fuel pressure on a Subaru, you will need to locate the fuel pressure gauge, which is usually found near the fuel filter or the fuel injector rail. If you are having trouble finding the fuel pressure port, consider adding a tee to the supply hose coming off the filter to attach your pressure tester. Once you have located or created the appropriate attachment point, follow these steps:

1. Install the pressure tester when the engine is cold.

2. Turn the ignition key and then start the engine.

3. Record the pressure readings both at key turn and with the engine running.

4. For a car with a port-injected pump, the reading should be between 30 and 80 PSI. If it does not match the required pressure, your fuel pump may need attention.

5. Observe the gauge while revving the engine to further diagnose any issues.

Check the fuel pressure gauge

Checking the fuel pressure gauge on a Subaru vehicle requires some preliminary steps before the actual testing. Firstly, it is important to know the standard fuel pressure for your specific Subaru model, as this will serve as a benchmark for your readings. This information can be found in the owner's manual or through online model-specific forums.

Next, locate the fuel pressure gauge port on your Subaru. This is where you will connect your pressure tester. The port's location may vary depending on the model, but it is typically near the fuel filter or the fuel injector rail. If you cannot find a designated port, you may need to add a tee to the supply hose coming from the fuel filter.

Now, you can begin the testing process:

• Ensure the engine is cold before you start.
• Install the pressure tester onto the test port.
• Turn the ignition key and then start the engine.
• Observe and record the pressure readings both at idle and when the engine is running.
• For a Subaru with a port-injected pump, the standard reading should be between 30 and 80 PSI.
• If the reading does not match the required pressure, further inspection is needed, and you may need to take your car for servicing.

Additionally, here are some general tips for checking fuel pressure:

• You can check the fuel pressure gauge while someone else revs the car, allowing you to observe any changes in pressure.
• Fuel pressure should increase as the engine RPM increases.
• Basic fuel pump operation can be verified by observing the gauge reading while cranking the engine in a no-start condition. The fuel pressure should be approximately 21 PSI.
• If you suspect an issue with the fuel pressure regulator, you can disconnect the vacuum hose from the regulator and observe any changes in the gauge reading.

Remember to always exercise caution when working on your vehicle and refer to your owner's manual or seek professional assistance if you are unsure about any steps.

Observe the temperature gauge

To check the fuel pressure on a Subaru, you will need to observe the temperature gauge. This is because the temperature of the car can help predict a fuel pump emergency. If the heat rises and the car stalls, pay attention to your temperature gauge as this may indicate that the fuel pump motor is malfunctioning. If the car continues to stall out, the fuel pump will deteriorate and need to be replaced.

The temperature gauge can also help you identify a problem with the fuel pump's relief valve. If the relief valve fails to open, more fuel than necessary will flow into the engine system. If your vehicle normally gets good gas mileage and then suddenly becomes a gas guzzler, there could be an emergency under the hood. In this case, the temperature gauge may indicate abnormal temperature readings.

Additionally, observing the temperature gauge can help diagnose issues with the fuel pump motor. If the gas pedal is depressed and the vehicle surges forward out of nowhere, this could be due to irregular resistance within the fuel pump motor. The temperature gauge may show fluctuations or abnormal readings during such events.

Furthermore, the temperature gauge can provide insights into potential fuel pump failure. If the engine sputters at high speeds, it could be an indicator of a struggling fuel pump. The temperature gauge may show unusual patterns or deviations from normal temperature readings in such cases. By closely monitoring the temperature gauge and noticing any abnormalities, you can take proactive measures to address potential issues with your Subaru's fuel system.

Monitor how often you refuel

Monitoring how often you refuel is an important aspect of car maintenance. While it may be tempting to keep your tank as empty as possible to save on petrol, this can actually be detrimental to your car's health.

Firstly, it's important to note that modern cars have an in-tank fuel pump that needs to be kept cool, and fuel helps with this. Running your tank too low can cause this pump to overheat and fail, leading to a standstill. Additionally, the fuel pump has a relief valve, and if this fails to open, more fuel than necessary will flow into the engine system, resulting in reduced fuel efficiency.

Secondly, letting your tank get too low can cause damage to your vehicle. Modern cars have a "gas bag" inside the fuel tank to contain vapors. If the tank gets too empty, this bag can collapse and may not expand properly when you refill it. It is generally recommended that you keep your tank above a quarter full to avoid these issues.

Other factors to consider include the weather conditions and the type of roads you're driving on. If you're driving in cold weather, it's a good idea to keep your tank at least a quarter full to avoid potential issues. Similarly, if you're driving on dusty or rough roads, or in extremely hot or cold weather, it's recommended to service your Subaru more frequently, which includes monitoring your fuel levels and refuelling more often.

In addition to the above, keeping an eye on your fuel consumption can help you identify any potential issues with your car. For example, if your vehicle usually gets decent gas mileage but suddenly becomes a gas hog, it could indicate an emergency under the hood, such as a failing fuel pump or a clogged fuel filter.

Therefore, it is advisable to monitor your fuel levels regularly and refuel when your tank reaches half or quarter full. This will help ensure the optimal performance of your vehicle and prevent any potential issues or emergencies.

Test the fuel pump

To test the fuel pump of your Subaru, you will need to check the fuel pressure. Here is a step-by-step guide on how to do this:

Firstly, locate the fuel pressure gauge port. This can usually be found on the fuel injector rail, but if you are unsure, check your manufacturer’s guidelines. If there is no test port, you will need to add a tee to the supply hose coming off the fuel filter. You can then attach your pressure tester to this.

Next, install the pressure tester to the test port. Ensure the engine is cold before you begin. Then, turn the ignition key and start the engine. Record the pressure readings both at idle and when the engine is running. For a car with a port-injected pump, the reading should be between 30 and 80 PSI. If the pressure is lower than this, your fuel pump may be failing.

If you are still unsure, you can try another test. Start by removing the fuel pump fuse and running the engine until it stalls. Crank the engine for another five seconds, then turn the key off and reinstall the fuel pump fuse. Next, disconnect the fuel filter outlet hose and connect a fuel pressure gauge between the fuel filter outlet and the hose. Start the engine and idle.

Now, disconnect the vacuum hose from the pressure regulator. Pinch the return hose closed and observe the gauge reading. This checks the fuel pump's maximum output pressure. If the pressure is not within the manufacturer’s specifications, check the delivery lines. If they are not pinched or restricted, you may need to replace the fuel pump.

Check for low pressure in the fuel line

Checking for low pressure in the fuel line is an essential step in fuel pump testing and can help you diagnose potential issues with your Subaru. Here is a step-by-step guide on how to do it:

Step 1: Prepare the Car and Gather Tools

• Park your Subaru in a well-ventilated area and put on safety gear, including gloves and safety goggles, as you will be working with flammable fuel vapours.
• Ensure the engine is cold.
• Locate the Schrader valve fitting on the fuel rail. It may be hidden under a fuel rail cover or other plastic engine cover.
• Remove the Schrader valve cap.

Step 2: Attach the Fuel Pressure Tester

Attach the appropriate fuel pressure tester fitting to the Schrader valve. Ensure it is threaded on properly for a leak-proof fit.

Step 3: Check Fuel Pressure

• Turn the ignition to the "on" position (do not start the engine).
• Check the psi reading on the fuel pressure tester gauge.
• Observe the gauge for a psi drop, which would indicate a leak in the system.
• If the pressure remains steady for 5-10 minutes, the system is holding pressure well.
• If the pressure drops (e.g., losing 20 psi in 10 minutes), there is a leak in the fuel system.

Step 4: Start the Engine and Observe

• Start the engine and let it idle.
• Observe the fuel pressure gauge. You should see steady fuel pressure, within a few psi of the recommended pressure for your specific Subaru model.
• Slowly rev the engine and observe if the pressure rises with RPMs.
• If the fuel pressure holds steady and rises with engine speed as expected, your engine problem is likely not fuel-related.

Step 5: Diagnose Low Fuel Pressure

If you observe low fuel pressure, there are several potential causes to investigate:

• Clogged fuel filter: If the fuel filter is clogged, it can restrict fuel flow and cause low pressure. Consider replacing the fuel filter, especially if it has been over 20,000 miles since the last replacement.
• Failing fuel pump: If the fuel pump is not functioning properly, it may not be able to deliver fuel at the required pressure. Check the fuel pump for power and proper functioning using a multimeter.
• Improper tank venting or a loose gas cap: Ensure the gas cap is tight and the gasket is not damaged. A loose or faulty gas cap can cause emissions issues and affect fuel pressure.
• Other potential issues: Low fuel pressure can also be caused by a faulty fuel pressure regulator, a clogged or kinked fuel return line, or issues with the fuel pump driver module or powertrain control module.

By following these steps and troubleshooting potential causes, you can effectively check for low pressure in the fuel line of your Subaru and take appropriate action to resolve any issues.

Frequently asked questions