Katerina Swanson
Purging a fuel line is an important process that helps to ensure the smooth running of an engine. It involves removing air and debris from the fuel system, which can cause issues such as fuel starvation and engine shutdown. The process varies depending on the type of engine and fuel system, but typically involves opening the fuel lines, bleeding air and fuel out of the system, and replacing fuel filters. For those with electric pumps, it is recommended to power up the pump and let it run for a minute to flush out debris, while those with mechanical-lift fuel pumps can use a small lever to pump fuel without starting the engine. This process is crucial for diesel engines, where air in the fuel system can lead to simultaneous engine and generator shutdown.
Fuel Line Purging Characteristics and Their Values:
| Characteristics | Values |
|---|---|
| Fuel Line Purging Method | Blowing into the disconnected fuel line on the carburetor side |
| Fuel Type | Diesel, Gasoline with Ethanol |
| Tools/Materials | Fuel hose, gasoline can/safe container, gum-out, coarse and fine filters |
| Engine Type | Mechanical fuel pump, Electric pump |
| Steps | Remove filters, place fuel line end in a safe container, power pump, crank engine, replace filters, reconnect fuel line |
| Precautions | Avoid using compressed air due to fume dangers, check rubber lines for swelling, avoid bursting carburetor diaphragms by using priming lever/bulb |
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What You'll Learn
Bleeding a diesel fuel system
Firstly, identify how air entered the system. Diesel engines should never run dry, as this can cause an airlock, which will interrupt the flow of fuel and cause the engine to shut down. Before bleeding, inspect the connection points and the fuel line for any leaks, and correct these issues.
If your engine has a mechanical-lift fuel pump, it will likely have a small lever that allows you to pump fuel without turning on the engine. To purge air from the low-pressure side of the fuel system, open the fuel-line unions and bleed ports downstream of the pump, one at a time, starting with those closest to the pump. Continue pumping until fuel, not air, runs out. If your engine has an electric pump, turn the ignition key to the 'on' position to activate the pump, and allow it to run for about a minute.
The secondary or on-engine fuel filter is often where air becomes trapped. Most secondary fuel filters have a bleed screw. Loosen this screw by half a turn, and then use the lift-pump lever until a clear stream of fuel flows out. You may need to loosen the screw further, but do not pull it out. Three to four turns is usually enough. Once loosened, the next step will be messy, so have plenty of rags on hand.
Next, bleed the injection pump and the individual injectors using the same procedure. Finally, crack open the fuel lines at the injectors to bleed air out of the high-pressure fuel system. Loosen the union nuts between the top of the fuel injectors and the fuel line by a turn or two. Then, use the starter to crank the engine for 10 seconds. If fuel does not appear, wait 60 seconds to let the starter cool, and then crank again for 10 seconds.
The process may need to be repeated several times until fuel dribbles out. When it does, tighten the unions and crank the engine with the throttle advanced by 25%. The engine should start, although it may run roughly at first. Adjust the throttle until the engine runs smoothly.
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Clearing lines with gum-out
To start the process, remove all the filters and bypass them with new pieces of fuel hose. This will ensure that the Gum-Out has a clear path to travel through the fuel lines. Place the end of the fuel line, just before the carburettors, into a gasoline can or another safe container. This will allow you to catch any fuel or debris that is flushed out of the lines.
If your car has a mechanical fuel pump, the next step is to remove the spark plugs and crank the engine over on the starter for about a minute. This will activate the pump, which will then move a large quantity of fuel through the pipes, flushing out any debris. If you have an electric pump, simply power it up and let it run for a similar amount of time.
After the fuel lines have been flushed with Gum-Out, it is important to fit new filters and ensure that all connections are secure before starting the engine. This process should effectively clear the fuel lines of any blockages and improve the performance of your vehicle.
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Using an electric pump
Purging a fuel line is necessary when there is air in the line, which can prevent the engine from starting.
If you have an electric pump, the process is straightforward. First, remove all the filters and put the end of the fuel line in a gasoline can or another safe container. Then, power up the electric pump and let it run for about a minute. The pump will move a large volume of fuel through the pipes, flushing out any debris. Once this is done, fit new filters and reconnect everything.
It is important to note that if you have a filter before the pump, it should be coarse rather than fine. A second, finer filter can be placed between the pump and the carburettor.
Additionally, always use calibrated gas detection equipment during purging operations to determine if natural gas is present. Do not rely on your sense of smell to detect natural gas, as it is colourless and odourless. Make sure to consult your local fuel gas code for specific requirements.
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Purging air from the low-pressure side
Purging the air from the low-pressure side of a fuel system requires a different approach depending on the type of pump in your engine. If your engine has a mechanical-lift fuel pump, it will likely be equipped with a small lever that lets you pump fuel without turning on the engine. To purge air from the low-pressure side of the fuel system, open the fuel-line unions and bleed ports downstream of the pump, one at a time, starting with those closest to the pump. Keep pumping until fuel, not air, runs out.
If your engine is equipped with an electric fuel pump, the procedure is similar. Instead of working a lever, turn the ignition key to the 'on' position to activate the pump. On some engines, the electric pump only runs when the glow plugs are operated or when the engine is running, so you may need to temporarily hot-wire the pump.
If you have an electric pump, power it up and let it run for about a minute. The pump will flush out debris and move a large amount of fuel through the pipes. Install your new filters and reconnect everything.
If you have a mechanical fuel pump, remove the spark plugs and crank the engine over on the starter for about a minute. Remove all the filters and bypass them with new pieces of fuel hose. Put the end of the fuel line (just before the carbs) in a gasoline can or another safe container.
The final step in bleeding air out of a diesel fuel system is to crack open the fuel lines at the injectors.
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Bleeding the high-pressure fuel system
Before initiating the bleeding process, it is essential to exercise caution. High-pressure fuel lines contain fuel under intense pressure, and any mishandling can lead to hazardous situations. Ensure that you wear appropriate protective gear, including eye protection and gloves, to safeguard yourself from potential fuel spray or spillage. Additionally, make sure that the work area is well-ventilated to prevent the buildup of flammable fumes.
The first step in bleeding the high-pressure fuel system is to successfully bleed the fuel up to the injection pump. This involves opening the bleed screw and working the lift pump lever until you observe a clear, air-free stream of fuel. This process should be performed carefully, ensuring that no air bubbles are present in the fuel stream. Once you have achieved this, you can move on to the next step.
The next critical stage involves bleeding the injectors. This step requires extreme caution as it entails working with high-pressure fuel lines. Begin by loosening any high-pressure fuel lines connected to the injectors, always being mindful of your hand and arm placement to avoid potential hazards. Crank the engine with these lines loosened, but ensure that your hands and arms are kept well away from these areas to prevent accidental contact with high-pressure fuel, which can cause serious injuries.
Finally, pay attention to the cranking duration. If you need to crank the engine for more than approximately 20 seconds to bleed the high-pressure fuel system, it is recommended to close the intake seacock. This precaution is necessary to prevent water accumulation in the exhaust system, which could eventually reach sensitive components such as the exhaust manifold and cylinders. Most trawler engine installations are designed to prevent this backflow, but it is crucial to follow manufacturer guidelines and comply with safety protocols.
By meticulously following these steps, you can effectively and safely bleed the high-pressure fuel system. Remember to consult manufacturer guidelines specific to your engine, as procedures may vary slightly between different models.
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Frequently asked questions
Purging refers to the introduction of an inert (i.e. non-combustible) purge gas into a closed system to prevent the formation of an ignitable atmosphere.
Purging helps to reduce the possibility of an explosion by ensuring that an ignitable mixture never forms.
Purging should only be done by a qualified professional in a well-ventilated area or by venting to the outside atmosphere. All sources of ignition in the area must be eliminated, and calibrated gas detection equipment should be used to check for the presence of gas.
Nitrogen and carbon dioxide are the most common purge gases commercially available in large quantities. Other inert gases such as argon or helium can also be used.
If your vehicle is experiencing fuel starvation or dying repeatedly, you may need to purge your fuel lines to flush out any debris or trash. Check the fuel filter and the rubber lines for any signs of blockage or swelling.
