Rajan Wilcox
The primer assembly in a Duramax engine is used to prime the fuel system by pumping diesel fuel from the tank into the filter. Over time, the O-rings in the filter head assembly can begin to allow air to bleed into the system, causing the fuel system to lose its prime. This can lead to fuel leaks and other issues. To remove the primer assembly from the fuel filter, you will need to purchase a repair kit, which typically includes a new fuel filter, O-rings, and other necessary components. The process involves disassembling the fuel filter housing, replacing the old primer assembly with the new one, and then reassembling the housing. It is important to note that this process requires basic mechanical skills and should be done carefully to avoid any damage to the engine.
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What You'll Learn
Locate the fuel filter housing
To locate the fuel filter housing on a Duramax engine, you must first identify the passenger side of the engine. The fuel filter housing is located on this side, below the air intake tube.
To access the fuel filter housing, you will need to remove the centre air intake tube, which is situated between the air filter housing and the turbocharger inlet mouthpiece. Once this is removed, you can then take out the passenger side inner fender, which is secured by plastic body clips. These clips can be fragile and prone to breaking, so take care when removing them.
With the inner fender removed, you will have clear access to the fuel filter housing. It is recommended to also attach a small section of fuel hose to the water-fuel separator drain valve, which is located at the bottom of the fuel filter. This will allow you to drain the water separator into a suitable container for proper disposal.
The fuel filter housing plays a crucial role in the fuel system, as it contains an integrated hand pump that is used to pump diesel fuel from the fuel tank into the filter. Additionally, the housing may feature a plunger or a primer pump, which is used to prime the fuel system after replacing the fuel filter. This step is essential to ensure that any air is bled from the system before starting the vehicle, as air can cause additional strain and excessive wear on the high-pressure injection pump.
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Remove the water-in-fuel sensor assembly
To remove the water-in-fuel sensor assembly, you will need to follow these steps:
First, locate the fuel filter housing, which is on the passenger side of the engine. Next, remove the centre air intake tube, which is found between the air filter housing and the turbocharger inlet mouthpiece. You will then need to remove the passenger side inner fender, which is secured by plastic body clips. These tend to break and are rarely reused, so replacements are inexpensive and easy to source.
Now you will need to remove the water-in-fuel sensor assembly from the bottom of the fuel filter. Use an appropriate wrench, socket, or pliers to do this. If the water-in-fuel sensor assembly is damaged, do not reuse it. Replace the o-ring on the water-in-fuel sensor assembly, which should be provided with the new fuel filter. Lubricate the water-in-fuel sensor o-ring with clean engine oil, then install it snugly onto the new fuel filter. Do not overtighten.
Finally, lubricate the new fuel filter gasket with clean engine oil and install it at the top of the fuel filter assembly. Do not fill the filter with diesel fuel. The fuel filter housing has an integrated hand pump that will be used to pump diesel from the fuel tank into the filter. Install the replacement fuel filter, ensuring that the water-in-fuel sensor connector does not become entangled with its surroundings. Install snugly by hand only, do not tighten with tools.
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Lubricate the water-in-fuel sensor o-ring
To lubricate the water-in-fuel sensor o-ring, you will need to follow these steps:
Firstly, locate the water-in-fuel sensor assembly at the bottom of the fuel filter. Use a wrench, socket, or pliers to remove it. It is important to note that if the water-in-fuel sensor assembly is damaged, it should not be reused. Once removed, replace the o-ring on the assembly with the new one provided.
Now, lubricate the water-in-fuel sensor o-ring with clean engine oil. Ensure that you do not overtighten it when installing it onto the new fuel filter. The o-ring should be installed snugly by hand. Lubricate the new fuel filter gasket with clean engine oil as well, and place it at the top of the fuel filter assembly.
Do not fill the new fuel filter with diesel fuel. The fuel filter housing has an integrated hand pump that will be used to pump diesel from the fuel tank into the filter. Install the replacement fuel filter, ensuring that the water-in-fuel sensor connector does not become entangled with surrounding components. Again, this should be installed by hand, without the use of tools, to ensure it is not overtightened.
Finally, locate and open the bleed valve towards the driver's side of the fuel priming pump. If desired, you can remove the bleed screw to inspect the o-ring. To prime the system, repeatedly pump the plunger on the top of the fuel filter housing until all air escapes and diesel fuel begins to flow out of the bleed screw. Tighten the bleed screw, clean up any spills, and start the engine to check for leaks.
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Repeatedly pump the plunger to bleed the fuel system
Repeatedly pumping the plunger is an essential step in bleeding the fuel system of a Duramax engine. This process is necessary to ensure the removal of air from the system, which can cause issues such as airlock and affect the engine's performance.
To begin the process of bleeding the fuel system, locate the fuel pump lever or plunger, which is integrated into the fuel filter housing on the passenger side of the engine. This plunger is used to prime the fuel system, especially important for Duramax diesels from 2001 to 2016 that do not have an electric lift pump.
Now, start pumping the plunger repeatedly. As you do this, pay attention to the bleed screw. You will notice bubbles forming as air escapes from the system. This air removal step is crucial to prevent additional strain and excessive wear on the high-pressure injection pump.
Continue pumping until you no longer see any bubbles and only clean, bubble-free fuel is present. At this point, tighten the bleed screw back down while maintaining pumping to prevent air from re-entering the system. If there is a secondary fuel filter present, repeat this process with it.
After successfully bleeding the fuel system, you can start the engine and check for any leaks. If the engine runs rough for an extended period, turn it off, re-bleed the system, and check again for leaks, including at the bleed screw.
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Check for leaks
After reassembling the primer assembly, it is important to check for leaks. Start the engine and observe how it runs. If the truck runs rough for an extended period, turn off the engine, re-bleed the system at the fuel filter housing, and check for leaks, including the bleed screw o-ring. Look for fuel puddles on the ground or on top of the filter assembly, which could indicate external fuel leaks.
Early signs of a leak include extended cranking after the truck has been sitting for long periods, as well as the engine starting and then dying. As the problem progresses, it may become impossible to restart the truck without manually priming it when parked on an incline. This is because, over time, the O-rings in the filter head assembly can begin to allow air to bleed into the system, causing the fuel system to lose its prime.
If you suspect that your Duramax-powered truck is losing its prime or leaking fuel, it is important to address the problem as soon as possible. While your dealer may suggest replacing the entire assembly, there are less expensive solutions available, such as repair kits that require only hand tools and basic mechanical skills. These kits can include replacement O-rings, which are often the source of the problem, as well as other components like bleeder screws and fuel filters.
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Frequently asked questions
The primer assembly can be removed by following these steps:
- Removing the water-in-fuel sensor assembly from the bottom of the fuel filter using a wrench, socket, or pliers.
- Replacing the o-ring on the water-in-fuel sensor assembly.
- Lubricating the new o-ring and installing it onto the new fuel filter without overtightening.
- Lubricating the new fuel filter gasket and installing it at the top of the fuel filter assembly.
- Pumping the primer plunger repeatedly until it becomes firm.
- Starting the engine and checking for leaks.
Some early signs of a leaky primer assembly include extended cranking after the truck has been idle for long periods, and the engine starting and then dying. As the problem progresses, external fuel leaks may occur, which can be identified by fuel puddles on the ground or on top of the filter assembly.
Merchant Automotive offers a Master Filter Head Kit that includes a new OEM fuel filter, a billet aluminium water-in-fuel plug, a billet aluminium filter head spacer kit, a billet aluminium bleeder screw, and replacement O-rings. This kit is available for around $100. They also offer less expensive solutions, with kits starting at $20 for replacement O-rings.
Instead of removing the primer assembly, you can choose to rebuild it. This process involves purchasing a fuel primer rebuild kit, which includes an aluminium bleeder screw to replace the factory-installed plastic screw, and following a step-by-step guide or watching an instructional video.
