Sylvie Willis
Fuel injection systems are known to be more reliable than carbureted systems, but they are also more complex. This is because they require higher fuel pressures and often a fuel return line, which is not usually found in a carbureted vehicle. Fuel injection return lines are a common source of fuel leaks, so it is important to know how to install them correctly. The installation process can vary depending on the vehicle and the type of fuel injection system being used, but there are some general guidelines and best practices to follow.
How to Install a Fuel Injection Return Line
| Characteristics | Values |
|---|---|
| Return line size | Generally, return line size should be larger than the supply line. However, if the regulator is in the EFI unit, a larger return line may not be necessary. |
| Materials | Braided hose, nylon, or stainless steel are commonly used materials for the return line. Braided hose is rated up to 350 psi for nylon and 1,000 psi for stainless steel. |
| Fittings | Fittings should match the type of hose used and can be installed on a flush-cut length of hose. Specific fittings, such as Earl's EFI Vapor Guard hose and clamps, may be required for certain fuel injection systems. |
| Tools | A double flare tool is useful for creating hard metal lines, and a special tool is needed for GM OEM nylon line. |
| Pressure | Fuel injection systems require higher fuel pressures than carbureted systems. A high-pressure pump, typically an in-tank pump, is necessary. |
| Fuel filters | Fuel filters are recommended as fuel injectors can be sensitive to dirt. |
| Orifice or regulator | An orifice or regulator is required to prevent gas from blowing back into the tank instead of through the seat orifice in the carb. |
| Vehicle-specific considerations | For most V-6, I-6, and V-8 engines, a 3/8-inch fuel line is appropriate, while 5/16-inch may suffice for smaller engines. For high-horsepower V-8 engines, consider a 5/8-inch line. |
| Leaks | Fuel injection return lines are a common source of fuel leaks, especially on Duramax engines. Regular inspection and replacement of degraded components are essential. |
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What You'll Learn
Using the right materials
The materials you will need for installing a fuel injection return line will depend on your vehicle's make and model, as well as the type of fuel injection system you are installing.
Most fuel injection systems require higher fuel pressures than carbureted systems and will need a fuel return line. The size of the return line is important and will depend on the size and flow of the pump, injector flow, and fuel flow demand of the engine. The return line should always be larger than the supply line. For most V-6, I-6, and V-8 engines, a 3/8-inch fuel line is appropriate, and 5/16-inch will suffice for smaller engines. For a high-horsepower V-8, you may need a 5/8-inch line and hose.
You can use a braided hose for the fuel injection return line, which is generally rated for up to 300 psi and can go up to 350 psi for nylon or 1,000 psi for stainless steel. Braided hoses can also be used for other higher-pressure fluid systems like transmission coolant lines or power steering return lines. If you are using a braided hose, you will need to use matching fittings, which are designed for the specific type of hose.
Another option is to use a hard metal line, which is what vehicle manufacturers typically use for the long distance from the back of a 4x4 (where the tank usually is) to the front of the 4x4 (where the engine usually is). Metal lines hold pressure very well and can withstand high heat and abrasion. To build a system with hard metal lines, you will need a double flare tool and bendable lengths of hard metal line, as well as double flare couplers and AN fittings.
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Sizing the return line
Firstly, it's important to understand that the size of the return line can impact fuel pressure and flow. A return line that is too small can restrict fuel flow, leading to potential issues with fuel pressure regulation. Therefore, it is generally recommended to have a return line that is at least 5/16 inches, with some suggesting a minimum of 3/8 inches. This ensures that the return line can accommodate the fuel flow and prevent excessive restriction.
The size of the return line should also consider the engine's fuel consumption, especially for high-performance engines. Big HP engines, for example, consume a large amount of fuel, and the return line must be sized correctly to handle the volume of fuel from the high-pressure/high-volume fuel pumps. If the return line is too small, the high fuel volume can overwhelm it, leading to potential issues.
Additionally, the return line size should be compatible with the supply line and the fuel pump. Some sources suggest that the return line should always be larger than the supply line to accommodate the fuel flow. This is because the return line needs to handle the fuel volume from the pump and ensure unrestricted flow back to the tank. However, it's important to note that factory return lines are typically not larger than the supply lines, and going bigger may add unnecessary weight and cost without providing any significant benefits.
When sizing the return line, it's also essential to consider the material and type of line used. Metal lines, for example, hold pressure well and are highly durable, but they require flexible connections to the fuel tank and engine. Braided hose is another option, with nylon-braided hose rated at 300-350 psi and stainless-steel braided hose rated at up to 1000 psi. The choice of material depends on factors such as pressure ratings, compatibility with fittings, and cost.
Lastly, it's worth mentioning that if you're upgrading an existing fuel system, it's generally recommended to replace deteriorated parts with the same size parts. Changing the size of the return line may not always be necessary, especially if the previous setup was functioning correctly. However, if there are issues with fuel pressure or flow, resizing the return line might be part of redesigning the entire system.
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Installing a regulator
For factory fuel-injected vehicles, the pressure regulator is located inside the fuel tank on a returnless fuel system. In contrast, for return-style systems, the regulator is usually in the engine compartment near the fuel rails, with the return line from the rails or regulator routed back to the tank. In carburetor applications, the regulator is located in the engine compartment before the fuel filter and carburetor.
If you are using an aftermarket fuel injection, the fuel pressure regulator with the return line can be mounted directly to one end of the fuel rail with the fuel supply on the other end. The regulator can also be mounted on the other fuel rail with the two fuel rails linked together. The feed from the gas tank enters the inlet of the regulator and exits to the carburetor fuel inlet to complete plumbing and installation.
For carbureted applications, a returnless system with a traditional-style regulator does not circulate fuel back to the fuel tank with a return line. Fuel is pumped to the regulator, where pressure is reduced, and then continues to the carburetor, where flow is controlled by the floats and needle/seat assembly. A deadhead-style regulator is another simple and popular regulator setup. It is placed between the fuel pump and the carburetor and uses a restriction to lower the fuel pressure by decreasing the fuel flow.
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Using a braided hose
Braided hose is a rubber hose with either a braided stainless or braided nylon exterior. It is more durable than plain rubber hose but has similar issues with long-term durability and fuel vapors. Braided hose is generally rated over 300 psi and up to 350 psi. It can be used on other higher-pressure fluid systems like transmission coolant lines or power steering return lines. However, they should not be used on power steering feed lines unless rated for appropriate pressures.
When using a braided hose for your fuel injection return line, it is important to consider the type of fittings and hose compatibility. The metal fittings need to be paired with a hose from the same manufacturer. For example, Summit Racing offers braided hose and fittings in black nylon or stainless steel that can be installed on a flush-cut length of matching hose. The hose can be challenging to push over the barbs of the metal fittings, but this is necessary to achieve high-pressure ratings.
If you are upgrading from a carburetor to EFI, you can utilize the factory hard metal line as the return line and construct a high-pressure feed line. The appropriate fuel line size depends on your engine type. For instance, a 3/8-inch fuel line is typically suitable for V-6, I-6, and V-8 engines, while a 5/16-inch line may be sufficient for smaller V-6 and I-6 engines.
Additionally, consider the specific requirements of your vehicle's fuel injection system. For instance, the Sniper fuel injection system recommends using Earl's Vapor Guard parts, including the fuel hose, fittings, and clamps. Ensure that the hose you select is compatible with the recommended fittings and clamps of your fuel injection system.
Finally, regular maintenance and inspections are crucial to prevent leaks and possible hose failure. Replace the injector return hose whenever you remove or replace your fuel injectors, and always carry spare parts and tools in your vehicle.
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Building a high-pressure feed line
When constructing a high-pressure feed line, it is crucial to consider the engine's fuel flow demands, pump size, and injector flow rate. The feed line's diameter will depend on these factors, with 3/8-inch fuel lines being suitable for most V-6, I-6, and V-8 engines, and 5/16-inch lines sometimes being adequate for smaller engines. For high-horsepower V-8 engines, a larger 5/8-inch line may be necessary.
The choice of materials for the high-pressure feed line is also important. Braided hose, for instance, is often rated for pressures over 300 psi and can go up to 350 psi for nylon or even 1,000 psi for stainless steel. Additionally, the fittings must match the chosen hose to ensure a secure connection. It is recommended to use specialised clamps, such as Earl's Vapor Guard hose clamps, to secure the hose and fittings.
When installing a high-pressure feed line, it is also worth considering the return line. The return line should typically be larger than the supply line to accommodate high-volume pumps and prevent fuel from being blown back into the tank. However, if the regulator is built into the EFI unit, a larger return line may not be necessary, as there will be minimal flow and pressure in the line.
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Frequently asked questions
The size of the return line depends on the size/flow pump, injector flow, and fuel flow demand of the engine. A larger return line is required for big HP engines as they consume a large amount of fuel. A 3/8-inch fuel line is appropriate for most V-6, I-6, and V-8 engines, and a 5/16-inch line will usually suffice for smaller V-6s and I-6s.
Braided hose is generally rated over 300 psi and up to 350 psi (nylon) or 1,000 psi (stainless steel) using matching fittings. GM OEM nylon line is also a good option.
It is important to ensure that the system won't leak. Metal lines are recommended as they hold pressure well and can withstand high heat and abrasion. Fuel filters are also important as fuel injectors do not function well with dirt.
Fuel injection return lines, hoses, and fittings are a common source of fuel leaks on Duramax engines. It is important to closely inspect these components during any major service and replace them if they show signs of degradation.
