Checking Fuel Pressure: A Guide To Testing Fass Systems

Checking your FASS fuel pressure is an important part of maintaining your vehicle. FASS fuel pressure issues can cause a range of problems, from a simple fix like a blown fuse to a more complex issue like a clogged fuel filter or a faulty pump. To check your FASS fuel pressure, you'll need to follow a few steps, including inspecting the fuel filter, performing a '5-gallon bucket test', and checking for leaks in the fuel line. It's also important to refer to the recommended service life for your specific FASS system and ensure that you're using the correct type of filter.

Using a fuel pressure tester

Step 1: Prepare Your Vehicle

Park your vehicle and apply the parking brake. Ensure the engine is turned off and allowed to cool down completely. This step is crucial for your safety and to ensure an accurate reading.

Step 2: Locate the Fuel Pressure Test Port

Find the fuel pressure test port, usually located near the fuel injectors. Place a rag under the test port to catch any fuel that may be released during the testing process.

Step 3: Attach the Fuel Pressure Tester

Install the pressure tester securely onto the test port. Ensure that it is attached properly to prevent any leaks.

Step 4: Start the Engine and Record Pressure Readings

Turn on the ignition and start the engine. If your vehicle has specific RPM requirements for pressure testing, follow those instructions. Record the pressure readings on the fuel pressure tester gauge.

Step 5: Compare Readings to Specifications

Compare the recorded pressure readings to the manufacturer's specifications, which can be found in your vehicle's owner's manual. Ideal fuel pressure levels typically range from 30 to 80 PSI, but this may vary depending on the engine and vehicle model.

Step 6: Interpret the Results

If the fuel pressure readings are lower than specified, it could indicate a weak fuel pump or a clogged fuel filter. If the readings are higher than expected, it may suggest a failing fuel pump driver or a malfunctioning fuel pressure regulator.

Step 7: Take Appropriate Action

If the fuel pressure tester indicates an issue, further diagnostics and repairs may be necessary. In some cases, you may need to consult a professional mechanic for assistance.

It is important to note that fuel is highly flammable, so ensure you work in a well-ventilated area and take the necessary safety precautions, such as wearing safety glasses and gloves.

Additionally, before using a fuel pressure tester, ensure your fuel tank has at least two gallons of fuel, and confirm that your fuel pump is functional.

Checking the fuel pump fuse

Locate the Fuse Box: Start by locating your vehicle's main fuse box. It is usually positioned underneath the hood, near the front of your vehicle. However, some vehicles may also have a smaller fuse box located under the steering column inside the car.

Identify the Fuel Pump Relay: Open the cover of the fuse box and look for the fuel pump relay. It is typically coloured green or grey. Refer to your vehicle's manual if you're unsure about its location.

Remove the Relay: Grab the fuel pump relay firmly on both sides and pull it straight up to remove it from the fuse box terminals. If it feels stuck, try rocking it gently back and forth to loosen the connection before pulling it out. Removing the relay will prevent the fuel pump from functioning, so your engine won't start temporarily.

Clean the Relay Prongs: Hold the relay upside down and inspect the prongs for any rust or corrosion. Use a wire brush to scrape off any corrosion firmly. Alternatively, if the corrosion is stubborn, you can use an electrical contact cleaner. Wet a cloth with the cleaner and rub it onto the prongs.

Test the Relay: You can test the relay using a multimeter. First, locate the circuit diagram on the relay and identify the "power" prongs, typically labelled as 85 and 86, and the prongs to be tested, usually 87 and 30. Set your multimeter to the ohm setting (Ω) to measure the resistance.

Connect Jumper Wires: Attach jumper wires to the terminals of your vehicle's battery. Clip one wire to the positive terminal and the other to the negative terminal. Ensure you don't touch the ends of the jumper wires together to avoid creating a spark.

Connect the Relay: Flip the relay over so the prongs face upwards. Connect the jumper wire from the negative terminal to the prong labelled 85, and the wire from the positive terminal to the prong labelled 86.

Listen for a Click: As you attach the second wire, listen for a clicking sound. This indicates that a switch on the internal circuit has closed. If you don't hear the click, unclip the wire, touch it to the prong repeatedly, then clip it back on.

Measure Resistance: Hold the multimeter probes against the remaining prongs on the relay, typically labelled 30 and 87. The multimeter will measure the resistance of the internal circuit between these prongs.

Check the Reading: A properly functioning relay will show a reading of 0 on the multimeter, indicating no resistance between the circuit points. If the reading is greater than 0, the circuit inside the relay is faulty and may need replacement.

If your relay tests functional and you still experience issues, there could be a different problem with your fuel pump or electrical system.

Checking the voltage at the pump

Firstly, locate the electrical connection at the FASS unit. This is usually found near the pump itself. Once you've identified the correct wires, it's time to break out a multimeter. Set the multimeter to measure voltage, and touch the probes to the appropriate connections. With the key turned to the "run" position, you should read around 12 volts at terminal number 85.

If you own a ’98.5-present Dodge Cummins, there's an extra step. You'll need to turn the engine over with the starter for one revolution to check for the correct voltage at terminal 85. This is an important step to ensure an accurate reading.

Now, let's move on to the pump itself. With the FASS unit still running, check for 12 volts at the electrical connection of the pump. This step confirms that the pump is receiving the correct voltage to function optimally.

If you find that the voltage readings are lower than expected, there could be a problem with the wiring or the power source. In such cases, it's important to consult a professional mechanic or a FASS technical support representative, who can guide you through further troubleshooting steps or recommend necessary repairs.

Additionally, it's worth mentioning that checking the voltage is just one aspect of maintaining your FASS fuel system. Regular servicing of the filters and separators, as well as priming the fuel pump, are also essential to ensure reliable performance and longevity. By following the recommended service intervals and procedures, you can help keep your FASS fuel system operating at its best.

Performing a drop test

Step 1: Prioritize Safety

Before you begin, it's crucial to prioritize your safety. Releasing fuel under pressure can be dangerous and may cause fires or injuries. Always wear protective gear, including safety glasses and gloves. Ensure you work in a well-ventilated area, and avoid smoking or having any ignition sources nearby.

Step 2: Check Fuel Pressure

Start your vehicle and let it idle. Install a fuel pressure gauge, taking care to follow the manufacturer's instructions for a secure connection. Run the fuel pump and note the pressure reading on the gauge. Compare this reading to the manufacturer's specifications for your specific vehicle. If the pressure is significantly lower than the recommended level, you may have a fuel pump issue or a clogged fuel filter.

Step 3: Perform a Fuel Volume Test

If the fuel pump is supplying sufficient pressure, the next step is to perform a fuel volume test to ensure the proper amount of fuel is being delivered to the fuel injectors. This can be done using a flowmeter, which is the most accurate method. If you don't have access to a flowmeter, you can perform a timed fuel delivery test using a glass measuring container.

Step 4: Collect a Fuel Sample

Start your vehicle and let it idle. Collect a fuel sample for a specified duration, typically around five seconds, with the pump running. Refer to your vehicle's manufacturer specifications to determine the expected fuel delivery rate. Compare the amount of fuel collected during the test to the manufacturer's specifications. If the pump is not delivering the expected amount of fuel, there may be an issue with the fuel pump or the fuel injectors.

Step 5: Calculate and Convert Units

Depending on your vehicle's specifications, you may need to convert units to ensure an accurate comparison. For example, you might need to convert milliliters per second to gallons per hour to determine if your fuel delivery rate is within the acceptable range.

Step 6: Analyze Results and Take Action

If your fuel pressure and volume tests indicate low pressure or insufficient fuel delivery, there could be a problem with your fuel pump, fuel filter, or fuel injectors. In such cases, it is recommended to consult a qualified mechanic or seek specialized advice for your specific vehicle to diagnose and resolve the issue.

Checking the filter

First, make sure you have the right tools and parts for the job. You will need a new filter, a fuel pressure gauge, and some locking pliers. It is also recommended to have a 5-gallon bucket on hand for testing. Before you begin, consult your owner's manual for the correct torque specs and any other vehicle-specific information.

Now, turn off the engine and locate the fuel filter. It is usually found near the fuel pump. Loosen the clamps on both sides of the filter using the appropriate tools. Be careful not to loosen the water separator at this stage, only the fuel filter.

Replace the old filter with a new one. Ensure that the material inside the new filter is a wire screen mesh. Do not use paper or cellulose filters, as they are not suitable for this application.

With the new filter in place, turn on the unit. Depending on your vehicle, you may need to bump the starter more than once. Allow the unit to run for 30 to 60 seconds. You should hear a change in the tone of the motor once the fuel reaches the pump.

As soon as you hear the change in tone, tighten the filter. If the filter is still not priming, there may be an issue with the brush motor, fuel level, or proper procedures may not have been followed. Answer the following questions: Does your unit have a serviceable brush motor? If so, ensure the serial number and specs match those in your manual.

Check your fuel level and ensure that it is sufficient. Also, double-check that you have followed all the recommended procedures correctly. If you are still experiencing issues, the water separator may be the culprit.

Remove the water separator and inspect it for any obstructions or sharp bends. Place your thumb over the separator's nipple to ensure that the line is clear. If you suspect there may be an issue with the water separator, it is recommended to perform the "5-Gallon Bucket Test" as described in the FASS Fuel Transfer Pump Troubleshooting guide.

By following these steps, you can effectively check and service the filter on your FASS fuel pump. Regular maintenance and inspections will help ensure optimal performance and longevity for your fuel system.

Frequently asked questions