Efi Mustang Fuel Pressure: What You Need To Know

Fuel pressure is an important aspect of a Mustang's performance, especially when it comes to EFI (electronic fuel injection) systems. The fuel pressure regulates the flow of fuel from the tank to the engine, and it plays a crucial role in maintaining the proper air/fuel ratio for combustion. The ideal fuel pressure for a Mustang with EFI can vary depending on various factors, such as the engine specifications, modifications, and power add-ons. In this discussion, we will delve into the intricacies of fuel pressure in EFI Mustangs and explore the factors that influence it, as well as provide insights into troubleshooting and optimizing fuel delivery for enhanced performance and efficiency.

Fuel injectors and their role

Fuel injectors are a critical component of modern automobiles, including the Mustang. They are responsible for injecting fuel into the engine, and play a crucial role in the vehicle's overall performance.

The injector atomizes the fuel and forces it directly into the combustion chamber, where it is ignited by a spark plug, causing an explosion that drives the vehicle. This process, known as fuel injection, ensures that fuel is delivered efficiently, providing maximum power while minimising fuel consumption and reducing pollution.

Fuel injectors are typically made of stainless steel and consist of a solenoid, a nozzle, and an injector body. The injector body holds a precisely designed capillary or passage for the flow of highly pressurised fuel. The nozzle has two openings: an inlet that draws fuel from the tank, and an outlet that sprays fuel into the combustion chamber. The solenoid, connected to the Electronic Control Unit (ECU) or Electronic Control Module (ECM), controls the opening and closing of the valve, regulating the fuel injection process.

There are two main types of fuel injectors: mechanically controlled and electronically controlled. Mechanically controlled injectors use springs and plungers to mechanically control fuel speed, quantity, timing, and pressure. On the other hand, electronically controlled injectors, also known as "smart" injectors, are governed by the ECM, which controls fuel quantity, pressure, and timing.

In terms of fuel injector types, there are diesel and gasoline fuel injectors. Diesel fuel injectors require much higher injection pressure (up to 30,000 psi) compared to gasoline injectors due to the heavier fuel. Gasoline injectors can be mounted in the intake manifold (multi-port injection or throttle body) or directly into the combustion chamber (GDI).

Fuel pressure at idle

Fuel pressure is an important aspect of a car's performance, and getting it right is crucial for a smooth idle. For Mustang owners, understanding the ideal fuel pressure at idle can help diagnose and prevent issues with their vehicles.

One common issue with Mustangs is a rough idle, which can be caused by low fuel pressure. A forum user with a 2018 Ford Mustang GT reported issues with rough idling, which led to stalling. The problem was diagnosed as low fuel pressure, and the solution involved checking the fuel pump and lines for any trash or blockages. This highlights the importance of maintaining proper fuel pressure to ensure a stable idle.

Another user with a vintage Mustang experienced a similar issue where their car would stumble when accelerating from idle. The fuel pressure at idle was measured at 33 PSI, and it dropped into the low 20s when throttle was applied. The recommended fuel pressure for a stock Mustang at idle is between 37 and 42 PSI, depending on whether the vacuum line is connected or not. In this case, the issue was potentially caused by a faulty fuel pump or a clogged filter, leading to insufficient fuel pressure.

It's important to note that fuel pressure regulators play a crucial role in maintaining the correct fuel pressure. A faulty regulator can cause inconsistent fuel pressure, leading to idling issues. When installing an EFI system, it is recommended to include a fuel pressure regulator in the return line to ensure proper fuel pressure control.

Additionally, when tuning a Mustang with a Holley carburetor, it's important to ensure that the fuel pressure is not too high. One user shared their experience where they had to reduce the fuel pressure from 7.2 PSI to 6.1 PSI to smooth out the idle and prevent the floats from sinking and overfilling the bowls. This highlights the delicate balance of fuel pressure required for a stable idle.

In summary, maintaining the correct fuel pressure at idle is essential for Mustang owners to prevent issues such as rough idling, stalling, and stumbling during acceleration. By regularly checking fuel pressure and addressing any issues with fuel pumps, lines, or regulators, Mustang owners can ensure a smoother driving experience.

Fuel pressure regulators

There are two common types of fuel pressure regulators: Pressure Reducing and Back Pressure. Pressure Reducing regulators control the downstream pressure and can be returnless or have a return line. On the other hand, Back Pressure regulators "bleed off" excess fuel through the return line to maintain the set pressure, controlling the upstream pressure.

When installing an EFI system, such as the MSD Atomic EFI, it is essential to consider the fuel pressure regulator setup. Some EFI systems, like the FiTech unit, have an internal regulator, while others may require an external regulator. Additionally, the vacuum line setup depends on the injector location. If the injectors are above the throttle plates, a vacuum reference is not required. However, if the injectors are below the throttle plates or in the intake manifold, a vacuum reference is necessary.

There are various aftermarket fuel pressure regulators available for Mustangs, such as the BBK Performance BBK 1706 and BBK 1707, which are fully adjustable and made from CNC machined billet aluminum. These regulators allow for fine-tuning of the fuel system to improve performance and achieve maximum horsepower. It is important to carefully install and monitor these regulators, as some users have reported issues with leaking fuel and diaphragm failure.

Fuel pump options

There are several fuel pump options for your EFI Mustang. You can choose from various brands and models, depending on your specific requirements and preferences. Here are some of the options available to you:

Holley EFI Fuel Pump Module

The Holley Sniper fuel pump module is a popular choice for EFI Mustang owners. It is a high-performance, easy-to-install option that directly replaces the factory fuel pump in the tank. This module comes in two versions: the 340 LPH and the 525 LPH, offering different horsepower support for both gasoline and E85 fuel types. It is compatible with E-85, ethanol-free gasoline, or a mix of both. It is made of black anodized 6061-T6 aluminum and features two -6 AN ORB Female fittings for installation flexibility.

Aeromotive Tank

The Aeromotive Tank is another option for your EFI Mustang. It offers an in-tank fuel pump solution, similar to the Holley option. This tank includes a fuel pump in the stock location, providing a clean and quiet operation without the need for external pumps.

Spectra Tank

The Spectra Tank is an EFI fuel tank option that includes an in-tank fuel pump. It is designed to fit in the stock fuel sender location. However, some users have reported issues with pump noise and failure, as well as the challenge of pump replacement if needed.

In-Line Fuel Pump

If you prefer an in-line fuel pump setup, you can consider using pumps from non-HO Ford vehicles such as T-birds, Crown Vics, and Towncars. These options are more affordable and can work as long as they can supply the required fuel pressure and volume. You can also look for in-line electric fuel pumps from vehicles like the F150, which are frame-mounted and easier to install.

External Sump and Two Pump Setup

This option involves using an external sump and two electric fuel pumps. It provides a quick and easy solution, but it may result in noise and undercarriage clutter issues due to the external pumps.

Fuel Accumulator

A fuel accumulator, such as the one offered by bcbroncos.com, can be used in conjunction with a low-pressure pump to maintain a reservoir of fuel and a high-pressure pump to supply fuel to the EFI system. It also acts as a filter and helps regulate fuel pressure.

When choosing a fuel pump option, consider factors such as ease of installation, noise levels, fuel compatibility, horsepower requirements, and your budget. Additionally, ensure that the fuel lines and fittings are compatible with the chosen fuel pump to avoid any issues with fuel pressure regulation.

Fuel lines and their routing

When it comes to EFI fuel line routing for a Mustang, there are a few things to consider. Firstly, it is important to use the correct size fuel line. While some people suggest using 3/16" tubing, this is not recommended as it is too small and can cause issues. Instead, opt for 5/16" or even 3/8" tubing, especially if you are making more power than stock.

Another important consideration is the material of the fuel line. Aluminum fuel lines are a good option, but it is crucial to use the correct end fittings. Flaring the ends is the best method, while compression fittings are a suitable alternative. Do not attempt to use rubber hose over a bare tube end as it will not hold under the high pressure of EFI systems.

Now, onto the routing of the fuel lines. There are a few different ways to do this, and it may depend on the specific model of Mustang you have. Some people choose to run the lines through the convertible passenger side inner rocker, attaching them to the bolts used for the brake line that runs through the tunnel. Others opt to run the lines along the subframe rails, either on the driver's side or passenger side, and then through a hole in the fender well to the engine. If you have a convertible, you may need to consider the space constraints behind the back seat when routing the lines.

One popular method is to run the pressure side line over the rear axle on the driver's side and the return side line over the rear axle on the passenger side. Then, bring the lines together near the passenger side of the driveshaft tunnel and run them up into the engine compartment. However, there are many ways to do this, so choose the route that works best for your setup.

When running the lines, try to keep them away from heat sources and tuck them close to the body. Additionally, consider using high-pressure clamps and hoses to secure the lines and prevent leaks.

Frequently asked questions