Adjusting Fuel Pressure: Fass 150 Basics

The FASS 150 is an aftermarket lift pump for diesel engines. The pump is designed to provide high volume and low pressure, but some users have reported issues with erratic or low fuel pressure. To adjust the fuel pressure on a FASS 150, you can try a few different methods. One way is to stretch the existing spring that regulates fuel pressure. This can be done by removing the hose/fitting connected to the air/vapor return to the tank and then stretching the spring by hand or with a tool. Another way to adjust the fuel pressure is to replace the spring with a different tension spring, such as a PS-1020 or PS-1008 spring. These springs can be purchased from FASS support or through a dealer. Additionally, some users have reported that replacing the hard plastic ball that creates a seal when the pump is off can help with fuel pressure issues. Finally, a fuel pressure regulator can be installed to adjust the fuel pressure, although this option may be more expensive and there are easier ways to accomplish the same thing.

Installing a fuel pressure gauge

Firstly, you will need to gather the necessary parts and tools. For this installation, you will require a 60 or 100 psi gauge, a gauge fitting for a 3/8 inch fuel hose, and two 3/8 inch hose clamps. It is important to note that while the fuel lines are actually 5/16 inch inside diameter hoses, the 3/8 inch gauge fitting will still fit. You can order these parts from specialist retailers or online.

Next, you will need to prepare the gauge for installation. Wrap the gauge's threads with two wraps of Teflon tape, ensuring that the tape does not extend below the threads. This will prevent any tape from getting into the fuel lines. Then, screw the gauge into the gauge fitting by hand. If it is too tight to do so by hand, use a large wrench or vise to hold the fitting and a small wrench to screw in the gauge.

Now, you will need to connect the gauge to the fuel line. Locate the fuel line closest to the oil dipstick. This is usually a rubber hose that connects to a metal pipe near the engine. Before cutting the hose, it is crucial to release the fuel pressure to avoid any spills or accidents. Once the pressure is released, cut the fuel line and use a rag to catch any fuel that may spray out. Have two 5/16 inch plugs or two Bic pen-type caps ready to stop the fuel flow.

After cutting the fuel line, remove the insulation tube that is wrapped around the fuel lines. This will allow you to fit the clamps onto the hose. Now, install the gauge and tighten the clamps.

Finally, you will need to prime the fuel system and check for any fuel leaks before starting the engine. Ensure that there is no pooled fuel anywhere and that all connections are secure. Normal idle fuel pressure should be between 28-32 psi.

It is important to note that you should never route a fuel line into the cockpit. If you are installing an electric pressure gauge, mount the pressure sender in the same way and route the output wire through the firewall to the gauge.

Adjusting the psi

The spring can be adjusted by stretching it, which will increase the fuel pressure. The amount of stretch required depends on the thickness of the spring wire. For example, a skinny-wired spring may need to be stretched by about half an inch to gain around 4 psi, while a thicker-wired spring will need less stretch to achieve the same pressure increase. It is recommended to make adjustments in small increments to avoid overdoing it.

Alternatively, you can replace the spring with a different tension spring. For example, replacing the stock spring with a PS-1020 spring can increase the pressure to 18-20 psi. These replacement springs are relatively inexpensive and can be purchased from FASS dealers or directly from FASS support.

It is important to note that adjusting the fuel pressure may not result in any noticeable performance difference. Additionally, CP3's were designed for vacuum operation and are not very sensitive to fuel pressure. Therefore, unless you have a specific reason for increasing the psi, it may not be necessary to make any adjustments.

Replacing the spring and ball

To replace the spring and ball on a FASS 150, you will need to remove the return line fitting on the unit. The spring is located under the check ball, which can be found by removing the hose/fitting connected to the "air/vapor return to the tank".

The spring can be inconsistent, causing erratic fuel pressure readings or lower-than-expected readings. If your spring looks twisted or deformed, you can either straighten it out and reinstall it or replace it entirely. Contact FASS support to obtain a replacement spring.

Regarding the ball, FASS uses a Buna ball, while Airdog uses a Viton ball. If you are experiencing issues with erratic or low fuel pressure, consider trying a Viton ball, as it is made of stronger material.

If you are still experiencing lower pressure issues after replacing the spring and ball, you can try shimming the spring to raise the pressure. Use a washer with the following measurements: OD: 3/4", ID: 3/8"-1/2". Place the washer between the fitting and the spring, NOT between the spring and the ball.

Troubleshooting low fuel pressure

Check the Fuel Filters and Separator:

Servicing the fuel filters and separators is crucial for optimal performance. Ensure that you replace the filters regularly, using wire screen mesh instead of paper or cellulose. The recommended service life for a FASS 150 is 50,000 miles.

Prime the Fuel Pump:

If your fuel pump is not priming properly, perform the "5-Gallon Bucket Test" as outlined in the FASS troubleshooting guide. This test helps isolate the unit and identify any issues with the water separator or suction line.

Inspect the Suction Line:

Check the condition of the suction line and ensure it is free of obstructions and sharp bends. A restriction on the suction side of the pump can lead to cavitation and increased noise from the pump.

Check for Air Leaks:

Inspect all connections and fuel lines for any signs of air or pressure leaks. A leaky unit can cause a break in the vacuum, resulting in fuel draining back into the tank.

Inspect the Spring and Ball Mechanism:

Remove the hose/fitting connected to the "air/vapor return to the tank" in the FASS system. If the spring is twisted or damaged, it can cause erratic fuel pressure readings. Consider replacing the spring or installing a washer to shim the spring and raise the pressure.

Contact FASS Support:

If you have tried the above steps and are still experiencing low fuel pressure, don't hesitate to contact FASS customer support. They can provide additional guidance and help identify any underlying issues with your specific system.

Additionally, here are some general tips for adjusting fuel pressure on a FASS 150:

• The fuel pressure should be set within the recommended range for your vehicle. For example, Duramax engines typically operate at 8-10 psi.
• Ensure that you are using the correct fuel filters for your FASS unit. Check the fuel filter cross-reference lists provided by FASS to identify compatible filters.
• If you encounter issues with the CP3/Regulator, consider replacing both components, as they work together to maintain proper fuel pressure.
• If you have recently installed a FASS 150 and are experiencing low fuel pressure, check for any restrictions in the fuel system, such as a clogged filter or screen.

Locating the spring and ball

Understanding the Spring and Ball Mechanism

Before we begin, let's understand the role of the spring and ball in your FASS 150. The spring and ball mechanism is a common way for FASS and Airdog electronic lift pumps to regulate fuel pressure. The spring provides tension to maintain the desired fuel pressure, typically between 16-18 psi for optimal performance. The ball, made of hard plastic (either Buna or Viton), creates a seal when the pump is off, preventing fuel from leaking or moving in the lines.

Now, let's get into the steps to locate the spring and ball:

• Accessing the FASS 150 Pump: Start by locating the FASS 150 pump in your vehicle. It is usually mounted near the fuel tank or along the fuel line. You may need to refer to your vehicle's service manual or seek assistance from a mechanic if you're unsure about its location.
• Identifying the Hose Fittings: Once you have located the FASS 150 pump, look for the hose fittings connected to it. These fittings are part of the fuel line and facilitate the flow of fuel in and out of the pump.
• Locating the "Air/Vapor Return to the Tank" Hose: Among the hose fittings, identify the one specifically labelled as "air/vapor return to the tank." This hose is responsible for returning excess air or vapour from the pump back to the fuel tank.
• Disconnecting the Hose: Carefully disconnect the "air/vapor return to the tank" hose from the pump. You may need to use appropriate tools, such as wrenches or hose clamps, to loosen and remove the hose safely.
• Revealing the Spring and Ball: With the hose removed, you will now have access to the spring and ball mechanism inside. Look inside the fitting and you should see the spring and ball assembly.
• Inspecting the Spring and Ball: Once you have located the spring and ball, carefully inspect them for any signs of damage, corrosion, or wear. This is important as issues with these components can lead to erratic or inconsistent fuel pressure.
• Replacing or Adjusting: If you notice any problems with the spring and ball, you may need to replace or adjust them. You can refer to FASS support or consult a mechanic for guidance on obtaining and installing the correct replacement parts.

Remember to exercise caution when working on your fuel system and always refer to professional guidance or service manuals if you're unsure about any steps. Working with fuel systems can be complex and requires a good understanding of the components involved.

Frequently asked questions