Mercedes Mullins
Bleeding fuel lines is the process of removing air from a fuel system to enable the engine to start. This can be done by using a fuel bleed tool, such as the Blue Print fuel bleed tool, or by manually bleeding the air out of the fuel rail. To manually bleed the air out of the fuel rail, one can use the schrader valve (bike air pump valve) by turning on the key and letting the fuel pump prime, then using a rag to push lightly on the valve.
How to Bleed Fuel Lines (Petrol)
| Characteristics | Values |
|---|---|
| When to bleed fuel lines | When the car will not start with fuel in the tank |
| Before bleeding fuel lines | Check your fuses and listen for the fuel pump |
| First step | Turn the key to the 'on' position (but not start) and let the fuel pump prime |
| Second step | After the fuel pump has cycled, use a rag to push lightly on the valve |
| Third step | Repeat the process of cycling and bleeding until you get straight fuel from the valve |
| Alternative method | Use the schrader valve to bleed the air out of the fuel rail |
| Bleeding a diesel fuel system | Use the Blue Print fuel bleed tool to remove air from the fuel system |
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What You'll Learn
Using a fuel pump to bleed air from fuel lines
Bleeding the fuel lines is necessary when there is air in the fuel system, which can cause the engine to start poorly or not at all. This can happen when you run out of fuel, have leaks in your fuel lines, or change your fuel filter.
Using a fuel pump to bleed air from the fuel lines:
Firstly, you need to identify the key components of the fuel system, including the fuel tank, fuel lines, fuel filter, and fuel injectors. Familiarize yourself with the engine and its layout. Then, turn off the engine and locate the fuel filter. Check if it has a built-in bleeder screw. If it does, position a clean rag or towel beneath the bleeder screw to catch any fuel spills, and slowly loosen the screw with a wrench or bleeder screw key in a counter-clockwise direction.
If your fuel filter does not have a bleeder screw, or you suspect air remains in the system, you may need to bleed the fuel system at the fuel injectors. Locate the engine's fuel injectors, which are usually connected to the fuel lines. Loosen the fuel line connection with a wrench or socket set. Turn the key to the 'on' position, but not start, to allow the fuel pump to run and prime the fuel system. You can then cycle the key to the 'on' position a few more times to draw out any trapped air in the fuel line, which will be pushed back into the tank.
For vehicles with mercuiser engines, the fuel rail return line returns to the filter instead of the tank. At the front of the engine, you will see the two fuel rails and their connection points to the injectors. Each rail has a port, one with a pipe plug and one with a schrader valve (bike air pump valve). When changing the fuel filter without refilling with fuel, use the schrader valve to bleed the air out of the fuel rail. Turn the key on and let the fuel pump prime, then use a rag to push lightly on the valve, as the fuel pressure will cause spraying. It will take a few cycles of priming and bleeding before you get straight fuel from the valve.
After bleeding the air from the fuel system, try to start the engine. If it starts, let it idle for a few minutes and observe if there is a rough idle or reduced power.
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Bleeding air from the fuel rail
Locate the Fuel Rail: Begin by locating the fuel rail, which is typically found at the front of the engine. On inboard models, you will see the two fuel rails with their connection points to the injectors. At the front of each rail is a port, one with a pipe plug and the other with a Schrader valve, usually capped with a black brass cap.
Prepare the System: Before starting the bleeding process, ensure that your fuel filter is in good condition and filled with fuel. If you've recently changed the filter, make sure the O-ring is properly installed in the housing. Additionally, check for any restrictions in the fuel supply line to the filter, as this can impact the bleeding process.
Prime the Fuel Pump: Turn the key to the "on" position, but not to the "start" position. Listen for the fuel pump to run, as it pressurizes the primary fuel system. Repeat this process a few times, turning the key off in between cycles. This will help prime the fuel pump and move fuel through the system.
Bleeding Process: Once the fuel pump is primed, it's time to bleed the air from the fuel rail. Use a rag to lightly press on the Schrader valve, being cautious of the fuel pressure. You may need to cycle the key and bleed the valve a few times until you see straight fuel coming out of the valve instead of air.
Check for Air Bubbles: To ensure that all air has been removed from the system, you can attach a clear hose to the jet start valve and run it back to the tank. This way, you can visually inspect the fuel and ensure it is clean and free of air bubbles.
Start the Engine: After completing the bleeding process, try starting your engine. It may take a few attempts for the engine to run constantly. If you encounter any issues, double-check the fuel filter, fuel lines, and injectors for any signs of restrictions or leaks.
Remember, always exercise caution when working with fuel systems, and if you're unsure about any steps, consult a qualified technician for assistance.
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Bleeding air from the injection pump
Firstly, you must find the injection pump. This is connected to the injection fuel lines, which help pump fuel into the diesel engine cylinders at high pressure. Once you have located the injection pump, you need to find the bleeder screw. This is usually located on the injection pump and has a small screw that can be loosened to release air. Follow the fuel lines, as the bleeder screw is often positioned for easy access during bleeding.
Next, open the bleeder screw. You may need to use a wrench to loosen it if it is too tight. Then, use a hand pump to pump the fuel system until clear, bubble-free fuel flows from the bleeder screw. Be careful, as the fuel is under high pressure and can be dangerous. Once the fuel is flowing smoothly without bubbles, tighten the bleeder screw again. Make sure it is closed tightly, as a poorly closed screw can cause fuel to leak, leading to damage.
Finally, start the engine to check that it is working correctly. You may need to repeat the process several times to ensure all air is removed from the system.
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Bleeding air from the injectors
First, it is essential to understand the function of the fuel system and the role of bleeding air from the injectors. The fuel system in your vehicle is responsible for delivering fuel from the tank to the engine, where it is injected into the cylinders for combustion. Over time, air can become trapped in the fuel lines, leading to reduced engine performance or even failure to start. Bleeding the fuel system involves releasing this trapped air, allowing fuel to flow freely again.
To begin the bleeding process, locate the fuel injectors. They are usually found at the front of the engine, connected to the fuel rails. Before proceeding, ensure that your vehicle is parked on a level surface and that the engine is switched off for safety. It is also recommended to wear protective gear, such as gloves and eye protection, to safeguard against any potential fuel spills or debris.
Once you have located the injectors, identify the bleeding valve or port. This is typically a small valve or plug located near the injectors. On some vehicles, it may be marked with a colour, such as brass, or have a cap for protection. Before proceeding, refer to your vehicle's manual or consult a mechanic to ensure you have identified the correct bleeding valve.
Now, you can start the bleeding process. Turn the key to the "on" position, but do not start the engine. This will activate the fuel pump, priming the fuel system and building up pressure. Let the pump run for a few seconds, and then turn the key back to the "off" position. Repeat this process a few times to ensure that the fuel system is pressurised and any trapped air is mobilised.
Finally, with the key in the "off" position, carefully open the bleeding valve using a suitable tool or your rag. Be cautious, as fuel may spray out due to the built-up pressure. Keep a safe distance and protect your eyes from any spraying fuel. After releasing the pressure, close the valve securely. Start the engine and observe its performance. It may take a few attempts to completely bleed the air from the system, so repeat the process if necessary.
Remember, always exercise caution when working with fuel systems. If you are unsure about any steps or feel uncomfortable performing the procedure, it is best to consult a qualified mechanic.
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Bleeding air from a diesel fuel system
Firstly, check for any leaks or clogs in the fuel lines and filters. Inspect the fuel lines from the tank to the lift pump and the fuel filters for any holes or damage that could cause an air leak. This step is crucial and should be done carefully. If your injectors are covered by a valve cover, use the appropriate mechanic tools to remove it.
Next, locate the secondary fuel filter, which is usually between the lift pump and the high-pressure injection pump. Most secondary fuel filters have a bleed screw. Open this bleed screw and work the lift-pump lever until you see a clear stream of fuel flowing out. This indicates that you have successfully bled the system up to this point.
Now, move on to the injection pump. Similar to the previous step, most injection pumps are also equipped with bleed screws. Open the bleed screw and use the starter to crank the engine for about 10 seconds. If fuel does not appear, wait for the starter to cool, and then crank again for a short duration.
Afterwards, bleed the high-pressure fuel system by loosening the union nuts between the top of the fuel injectors and the fuel line. Loosen the injection lines at the injectors by about one turn. Use two wrenches to prevent the binding or twisting of the steel lines. It is usually sufficient to bleed just half of the lines at a time.
Finally, crank the engine until all the air is forced out and fuel is present. The engine will start to pop on one or two cylinders. Tighten the injector lock nut one at a time to identify by sound which cylinders are firing correctly. Run the engine until it runs smoothly, indicating that all the air has been successfully bled from the diesel fuel system.
It is important to note that the procedure for bleeding a diesel fuel system may vary slightly depending on the manufacturer, but the basics outlined above will generally apply.
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Frequently asked questions
There are a few ways to do this. One way is to use the fuel pump by cycling the key to the "on" (but not "start") position a few times. You can also use a rag to put light pressure on the valve, but be careful because the fuel pressure is 32 psi. You could also try turning the key to "on" and listening for the fuel pump, which generally runs for 30 seconds to pressurize the primary fuel system. Turn the key off and repeat 5-6 times.
A fuel bleed tool is used to remove air from a fuel system to enable the engine to start. Blue Print has created a fuel bleed tool to remove air from a modern diesel engine.
A jet start valve is a valve on the side of the injection pump. You open it with a left turn to bleed the air out of the lines to the injection pump, then close the valve with a right turn.
If your car will not start, you may have vapor lock in the fuel line. Check your fuses and see if the pump is energizing when you crank it. If the pump is not moving fuel, air in the line will not be pushed through the lines, rails, and injectors.
