Adjusting Fuel Pressure: Returnless System Guide

Returnless fuel systems are a departure from traditional fuel systems, which start and end in the fuel tank and utilise one or more pumps to supply a high volume of fuel at high pressure to the injector rail. In contrast, returnless fuel systems supply only the fuel that is currently needed, eliminating the need for a return line. This has advantages for manufacturers, including reduced assembly costs and a reduced load on the evaporative emissions system.

Returnless systems work by pumping fuel from the fuel screen sock at the bottom of the tank to the fuel pump, which supplies the required fuel pressure and volume to the engine. The excess is then directed back into the tank after passing through a pressure regulator.

The pressure regulator in a returnless system is usually located inside the fuel tank, as opposed to in the engine compartment near the fuel rails in a return-style system. This relocation of the regulator helps to reduce evaporative emissions from the fuel system by eliminating the circulation of fuel between the engine and tank, keeping the fuel cooler.

Adjusting fuel pressure in a returnless system can be done by attaching a gauge to the service valve fitting on the fuel supply rail or by using a scan tool to look at the fuel pressure PID and measure fuel pressure.

Understanding the role of a fuel pressure regulator

A fuel pressure regulator is an essential component in a vehicle's engine management system. It plays a critical role in maintaining the correct fuel pressure, which is crucial for achieving optimal engine performance, fuel efficiency, and emissions control. By regulating fuel pressure, the regulator ensures consistent fuel delivery, smooth engine operation, improved fuel economy, and reduced environmental impact.

The regulator's primary function is to control the pressure of fuel supplied to the fuel injectors. It maintains a steady fuel supply, even during dramatic changes in fuel demand, by adjusting the fuel pressure against the air pressure or boost. This allows the fuel injector to maintain the perfect ratio between fuel and boost, ensuring a successful fuel and air mixture.

In a return-style fuel system, the regulator is typically installed between the fuel pump and carburetor or throttle body, while in a returnless fuel system, it resides inside the fuel tank. The regulator ensures that the fuel rail can build up enough pressure to support the injectors, preventing the fuel from flowing straight through without reaching the injectors. It also prevents the fuel pump from forcing too much fuel into the injectors, which would cause them to fail.

The optimal fuel pressure range varies depending on the type of engine. Carbureted engines typically have lower fuel pressures, ranging from 4 to 7 psi, while fuel-injected engines require higher pressures, usually between 30 to 50 psi. Turbocharged engines need even higher fuel pressures to meet the increased fuel demands under boost.

A fuel pressure regulator typically uses a spring and diaphragm mechanism to control fuel system pressure. It may be adjustable or preset, allowing for fine-tuning of the fuel pressure according to the engine's specific requirements. Maintaining the correct fuel pressure is essential for efficient fuel atomization, which breaks down fuel into small, uniformly distributed droplets. This ensures thorough mixing of fuel with air, promoting complete combustion and maximizing power output while minimizing fuel wastage.

In summary, a fuel pressure regulator is a critical component in a vehicle's fuel system, ensuring consistent fuel pressure, optimal engine performance, and improved fuel efficiency. By maintaining the correct fuel pressure, the regulator optimizes fuel atomization, combustion, and overall engine operation. Proper installation, regular maintenance, and inspection of the regulator are key to enhancing the performance and efficiency of the vehicle's fuel system.

The importance of maintaining correct fuel pressure

Maintaining the correct fuel pressure is of utmost importance for achieving optimal engine performance, fuel efficiency, and emissions control. Here are some reasons why:

Fuel Atomization

Fuel pressure plays a crucial role in ensuring proper fuel atomization, which is the process of breaking down fuel into small, uniformly distributed droplets. Efficient atomization allows for a thorough mixing of fuel with air, promoting complete combustion and maximizing power output.

Stoichiometric Ratio

Precise fuel pressure control ensures that the fuel-air mixture remains within the ideal stoichiometric ratio for efficient combustion. This minimizes fuel wastage and reduces harmful emissions by preventing the mixture from becoming too rich or lean.

Consistent Fuel Delivery

By regulating fuel pressure, a consistent fuel delivery is ensured, resulting in a smooth engine operation. This also improves fuel economy and reduces the environmental impact of the vehicle.

Engine Longevity

Maintaining the correct fuel pressure keeps the engine within the recommended levels, ensuring optimal performance, fuel efficiency, and longevity. This prevents potential damage caused by excessive fuel pressure or system overpressure.

Safety

Fuel leaks and vapor lock are two common issues that can occur when fuel pressure is not properly regulated. Fuel leaks pose a serious safety risk, as a small spark can cause a fire. Vapor lock, caused by fuel heating up and turning into gas, can lead to performance problems and reduced fuel efficiency.

How to convert a non-returnless fuel system to a return system

To convert a non-returnless fuel system to a return system, you will need to install a fuel pressure regulator with a return line. This setup allows excess fuel to be rerouted back to the fuel tank, maintaining consistent fuel pressure and preventing overpressure.

Firstly, you will need to determine the type of fuel system you currently have. Return-style fuel systems use a regulator to control fuel pressure, while returnless systems control pressure through the powertrain control module (PCM) and do not have external return lines.

If you have a returnless system, you will need to purchase and install the following components:

• A fuel pressure regulator with a bypass design
• A return line that connects the regulator to the fuel tank
• An external bypass fuel regulator with a return line to the top of the fuel tank (for aftermarket and race applications)
• An electric fuel pump that is mounted at or below the level of the bottom of the tank

If you have a factory setup or are assembling a custom system for a street rod or racecar, you may need additional components and modifications. It is recommended to consult a fuel system expert or a mechanic to ensure the conversion is done correctly and safely.

It is worth noting that converting from a returnless to a return system can be more complex and expensive than simply upgrading your existing returnless system, especially if you need to replace the fuel tank, pump, regulator, and return line.

Additionally, return-style systems have some drawbacks, such as a shorter fuel pump lifespan due to constant operation and a more complicated plumbing system due to the need for a separate return line. Therefore, carefully consider your specific requirements and seek professional advice before proceeding with the conversion.

The PCM's role in maintaining fuel pressure

The PCM (Powertrain Control Module) is the main computer in a modern vehicle that controls all its functions. It combines the ECM (Engine Control Module) and the TCM (Transmission Control Module) into one unit, allowing it to oversee and integrate the functions of both the engine and the transmission for optimal performance and efficiency.

In the context of a returnless fuel system, the PCM plays a crucial role in maintaining fuel pressure and ensuring the engine receives the right amount of fuel. Here's how:

Fuel Pressure Regulation:

The PCM actively regulates fuel pressure in the fuel rail by controlling the fuel pump's speed. It sends a duty cycle signal to the Fuel Pump Driver Module (FPDM), which in turn modulates the fuel pump's ground to rapidly turn it "on" and "off", adjusting its speed. This ensures that the fuel rail maintains the desired fuel pressure, typically around 40 psi.

Injector Pulse Width Adjustment:

On returnless fuel systems, the PCM ensures the engine receives the correct amount of fuel by making rapid adjustments to the injector pulse width. It can increase or decrease the duration of the injector pulses, allowing for precise control over the amount of fuel delivered to the engine.

Compensation for Fuel Temperature:

The PCM also takes fuel temperature into account. If it detects a rise in fuel temperature that could lead to vapor pockets in the rail, it will raise the target fuel pressure. The higher pressure counteracts vaporization, ensuring the fuel remains in a liquid state for proper combustion.

Pressure Sensor Feedback:

On newer fuel systems, a pressure sensor is employed to provide the PCM with real-time fuel pressure data. The PCM uses this information to make adjustments to the fuel pump's speed and the injector pulse width, fine-tuning the fuel pressure and volume accordingly.

Eliminating the Need for a Separate Regulator:

In some newer systems, the PCM's ability to monitor and adjust fuel pressure eliminates the need for a separate pressure regulator. This further streamlines the returnless fuel system design, reducing potential leak points and simplifying maintenance.

In summary, the PCM plays a critical role in maintaining fuel pressure in a returnless fuel system. By controlling the fuel pump and injector pulse width, compensating for fuel temperature, and utilizing pressure sensor feedback, the PCM ensures the engine receives the correct amount of fuel at the appropriate pressure for optimal performance, fuel efficiency, and emissions control.

How to service a returnless fuel system

Servicing a returnless fuel system requires careful handling to ensure proper function and full component life. Here's a detailed guide on how to service a returnless fuel system:

Understanding Returnless Fuel Systems

Returnless fuel systems are designed to supply only the fuel that is currently needed by the engine, eliminating the need for a return line. This offers two key advantages: reduced assembly costs and a lower load on the evaporative emissions system. In contrast, conventional fuel systems pump more fuel than is needed, leading to multiple trips between the tank and the engine, which adds heat to the fuel and contributes to fuel evaporation.

Servicing Considerations

When servicing a returnless fuel system, it is important to understand the placement of the fuel filter. There are three possible locations: outside the tank, in front of the pump (inside the tank), or after the pressure regulator. While placing the filter outside the tank is the easiest option for servicing, it can lead to contamination as the unused fuel is not filtered until its first trip to the engine. Placing the filter in front of the pump protects it from contamination but makes replacement more challenging. The last option, placing the filter after the pressure regulator, allows for repeated filtering of the unused fuel.

Fuel System Cleanliness

Fuel system cleanliness is of utmost importance, especially in returnless systems. Any dirt or debris left behind can quickly damage new components. It is crucial to inspect the fuel tank for any dirt, sediment, or rust particles that may be present. If necessary, steam cleaning the tank can help remove dirt and sediment. However, if a metal tank is rusty, it is recommended to replace the tank entirely to prevent future issues.

Fuel Pressure Checks

Fuel pressure checks on returnless systems can be performed by attaching a gauge to the service valve fitting on the fuel supply rail or by using a scan tool to monitor fuel pressure. It is also important to ensure that the fuel pressure regulator is functioning properly. In some cases, the regulator may need to be replaced, which requires accessing the in-tank fuel pump module.

Injector Maintenance

The injectors play a crucial role in the fuel system, and proper maintenance is essential. Over time, contaminants may build up in the fuel rail, affecting the injectors. Injector cleaning can be performed using fuel tank additives or on-car flushing equipment. If injectors are found to be severely clogged, they may need to be cleaned off-car or replaced entirely. Additionally, using "Top Tier" gasolines with higher levels of fuel system cleaning additives or periodic fuel injector cleaning can help maintain optimal performance.

Fuel Filter Replacement

The fuel filter in a returnless system may be located inside the tank, making replacement more challenging. In some cases, the entire fuel pump module may need to be replaced if the filter cannot be accessed separately. It is recommended to inspect the fuel tank for any signs of dirt or rust that could lead to a repeat failure of the new pump module.

Frequently asked questions