Increasing Fuel Pressure For Improved Engine Performance

FASS (Fuel Air Separation System) is a brand of diesel fuel pump designed to improve engine performance by removing air, water, and other contaminants from the fuel. While FASS fuel pumps typically do not come with a way to easily adjust fuel pressure, there are several methods that can be employed to increase fuel pressure. One common method is to adjust the regulator spring by stretching or shimming it. This can be done by removing the hose/fitting connected to the air/vapor return to the tank and accessing the spring and ball mechanism. Another method is to replace the existing spring with a stronger one, which can be ordered from FASS or purchased from a hardware store. It is important to note that increasing fuel pressure may not result in significant performance improvements and can, in some cases, cause issues such as engine loping if the pressure is too high.

Using washers to shim the regulator spring

To raise the fuel pressure on your FASS pump, you can use washers to shim the regulator spring. This is a straightforward process that can be completed in a few simple steps.

First, you will need to locate the regulator spring on your FASS pump. The regulator spring is situated behind the return fitting that sends excess fuel back to the fill neck. Once you have located the regulator spring, you can begin the process of shimming it with washers.

To shim the regulator spring, you will need to remove it from the pump. Take note of the rubber ball that seats on the backside of the spring, as you will need to ensure this does not get lost or damaged during the process. With the spring removed, you can now insert the washers. The number of washers you will need to insert will depend on your desired fuel pressure. For example, using two washers will increase the fuel pressure to around 90 PSI, while adding three or more washers will raise the pressure above 100 PSI. It is important to exercise caution when increasing the fuel pressure, as too much pressure can cause the bypass in the front cover to open.

Once you have inserted the desired number of washers, you can now reinsert the regulator spring back into the pump. Ensure that the spring is securely in place and that the rubber ball is properly seated. With the shimmed regulator spring in place, you have now successfully raised the fuel pressure on your FASS pump.

It is important to note that adjusting the fuel pressure on your FASS pump may void the warranty, so it is always a good idea to check with the manufacturer or a qualified mechanic before making any modifications. Additionally, it is crucial to use the correct type and size of washers to ensure a proper fit and avoid any potential damage to your pump.

Stretching the existing spring

To stretch the existing spring on your FASS fuel pump, you will need to first remove the return line fitting. This will expose the spring, which is located under the check ball. Once you have removed the spring, you can begin to stretch it. The amount you will need to stretch it depends on the desired increase in pressure. For example, one user reported that they needed to stretch the spring in their FASS 95 series by about 1/2" to gain around 4 psi. It is important to note that simply stretching the spring may not provide a long-lasting solution, as the spring may eventually return to its original shape, causing the fuel pressure to drop back down.

If you are unsure about stretching the spring, there are a few other options for increasing the fuel pressure on your FASS pump. One option is to insert a shim, such as a flat washer, between the pressure spring and the return fitting. This method can increase the pressure by a few psi and is easily reversible if you are not happy with the results. Another option is to install a fuel pressure regulator into the return line. This method may be more expensive, but it will allow you to adjust the pressure more precisely.

It is always a good idea to consult a professional or a FASS dealer if you are unsure about making any modifications to your fuel pump. They may be able to provide you with the correct psi spring for your specific pump and desired pressure. Additionally, they can guide you through the process to ensure that you are doing it safely and correctly.

Replacing the spring

To replace the spring on your FASS fuel pump, you'll need to first locate the spring. It is situated behind the return fitting that sends excess fuel back to the fill neck.

Once you have located the spring, you can remove it by taking off the hose or fitting connected to the "air/vapor return to the tank". Be careful not to drop the rubber ball that sits behind the spring when you do this. If your spring looks twisted or damaged, you should replace it with a new one of the same type. You can contact FASS support to get a replacement spring.

If you are looking to increase the fuel pressure, you can do so by ordering a stronger spring from FASS. Alternatively, you can try stretching the existing spring to gain more psi. This can be done by carefully pulling the spring apart, but be aware that stretching the spring may not be as effective as replacing it with a stronger one.

Another option to increase fuel pressure is to put a washer in to shim the spring. This should be placed between the fitting and the spring, not between the spring and the ball. Make sure you double-check the washer's inner diameter to ensure you're not adding any additional restriction.

Finally, if your FASS pump did not come with an adjustable regulator, you can try adjusting the pressure by using a different type of ball. FASS typically uses a Buna ball, but you can try an Airdog Viton ball, which is made of stronger material.

Ordering a stronger spring from FASS

Once you have identified the correct spring for your pump model, you can contact FASS directly to place an order. They offer support via phone and may be able to provide additional guidance on selecting the appropriate spring. Alternatively, you can purchase FASS springs from authorised dealers or online retailers. When ordering, ensure that you specify the correct spring part number to avoid compatibility issues.

It is important to note that adjusting fuel pressure can be a complex task, and incorrect adjustments may lead to engine problems. Always refer to the manufacturer's guidelines and consult with experienced professionals or mechanics before making any modifications.

Additionally, consider that increasing fuel pressure may not always result in significant performance improvements. In some cases, higher fuel pressure can lead to a decrease in the pump's flow rate, as observed in the FASS 150 series pump, where an increase in pressure from 8 PSI to 20 PSI resulted in a flow rate reduction from 150 GPH to 85 GPH. Therefore, it is essential to carefully consider the potential benefits and drawbacks of adjusting fuel pressure and consult with experts in the field to make an informed decision.

Adjusting the Allen head screw

To adjust the Allen head screw on your FASS fuel pump and raise the fuel pressure, you'll need to locate the screw and locknut, as well as the spring and ball that regulate fuel pressure.

First, find the Allen head screw and the accompanying locknut. The Allen head screw is likely a 5mm screw with a 14mm locknut, although this may vary depending on your specific pump model. It is typically located on the side of the pump housing.

Once you've located the Allen head screw and locknut, you can adjust the fuel pressure by turning the screw. Turning the screw will increase or decrease the pressure, depending on which way you turn it. Make sure to adjust the pressure in small increments to avoid over-tightening or under-tightening the screw, which can affect the pump's performance.

If your FASS fuel pump doesn't have an adjustable regulator, it likely uses a spring and ball system to regulate fuel pressure. In this case, you can adjust the pressure by stretching or shimming the spring. The spring is located behind the return fitting that sends excess fuel back to the tank. Before attempting any adjustments, make sure to consult a professional or the FASS support team to ensure you're using the correct tools and techniques for your specific pump model.

Additionally, the type of ball used in the spring and ball system can impact fuel pressure. FASS typically uses a Buna ball, while Airdog uses a Viton ball. You may need to experiment with different balls to find the one that works best for your pump and desired fuel pressure.

Remember to exercise caution when making any adjustments to your fuel pump, as incorrect adjustments can lead to performance issues or even damage to your vehicle. Always refer to the manufacturer's instructions or seek professional assistance if you're unsure about any steps or procedures.

Frequently asked questions