Bleeding Fuel Lines: Post-Filter Change For Duramax Vehicles

Bleeding the fuel system of a Chevy/GMC Duramax LLY engine is a crucial step after performing maintenance on the fuel injectors or fuel filter. This process ensures that any air trapped in the fuel lines is removed, preventing issues such as a rough idle or, in more severe cases, engine stalling. The bleeding procedure typically involves a combination of pumping the primer button or filter housing, cranking the engine, and carefully managing the bleeder screw on the filter assembly to release air and fuel. While the specific steps may vary depending on the vehicle's specifications and the extent of the maintenance performed, online forums provide a wealth of advice and experiences from Duramax owners who have successfully bled their fuel systems.

Ensure there's enough fuel in the tank

To ensure there's enough fuel in the tank when bleeding fuel lines after a filter change on an LLY Duramax, follow these detailed steps:

First, locate the fuel filter. It is typically found in the engine compartment on the passenger side or on the driver's side frame rail in front of the fuel tank. Before beginning any work, apply the parking brake for safety.

Next, you'll want to drain any water from the filter. Then, unplug the water sensor wire connected to the fuel filter and proceed to unscrew and remove the filter element. If there is any dirt on the filter sealing surface, be sure to clean it off. Now, remove and set aside the water sensor float switch, which is located at the bottom of the fuel filter.

At this point, you can install the new filter element. Reinstall and tighten the filter container, then reconnect the water sensor wire to the filter. Use the fuel filter primer to bleed air from the system. Locate the air bleed valve and tighten it by turning it clockwise until it's hand-tight.

Now, check to ensure there is fuel in the fuel tank. This is an important step to ensure a successful bleed and avoid airlocks in the system. With enough fuel in the tank, you can proceed to the next step, which is to start the engine and let it idle for approximately five minutes.

After the engine has idled for a sufficient amount of time, carefully check your fuel filter and air bleed valve for any signs of leaks. This step is crucial to ensure the safety and integrity of the fuel system.

By following these steps, you will help ensure that there is enough fuel in the tank when bleeding the fuel lines after a filter change on your LLY Duramax. Remember always to exercise caution when working on your vehicle and refer to a qualified mechanic if you have any doubts or concerns.

Install an electric lift pump

Installing an electric lift pump in your Duramax is a great way to ensure consistent fuel delivery and improve the longevity of your injection pump and injectors. Here's a step-by-step guide on how to install one:

Step 1: Purchase a Suitable Lift Pump Kit

Before beginning the installation, it's important to select a suitable lift pump kit for your Duramax. There are several options available, such as the PPE Lift Pump, FASS Titanium Signature Series, or AirDog II-4G. These kits typically include the pump, mounting hardware, fuel lines, and quick-connect fittings. They may also include additional fuel filtration and a water separator to remove contaminants from the fuel.

Step 2: Prepare the Vehicle

Park your vehicle on a level surface and engage the parking brake. Make sure you have all the necessary tools and safety equipment, including gloves and eye protection. Place a suitable container under the fuel filter to catch any spills or drips during the installation process.

Step 3: Access the Fuel System

Locate the fuel tank and the fuel lines running from the tank to the engine. You will need to disconnect the fuel lines and quick-connect fittings to install the lift pump. Depending on your vehicle and the kit you've chosen, you may need to remove the truck bed or drop the fuel tank for easier access. Be very careful when working with fuel lines to avoid spills and leaks.

Step 4: Mount the Lift Pump

Refer to the instructions provided with your lift pump kit for specific mounting instructions. Typically, the pump will be mounted on the driver's side frame rail using brackets that sandwich the truck's frame. Ensure that the pump is mounted securely and that there is no interference with other components, such as brake lines or parking brake cables. Drill any necessary holes and secure the pump assembly with the provided hardware.

Step 5: Connect the Fuel Lines

Now, you will need to splice the lift pump into the fuel system. Disconnect the fuel line from the sender to the hard line. Connect the input of the lift pump to the fuel tank using the provided fuel lines and quick-connect fittings. Then, connect the output of the pump to the input of the fuel cooler or injection pump. Be sure to use fuel line disconnect tools to release the recessed clips on the quick-connect fittings. Coat the barbed ends of the new fittings with oil before pressing the fuel lines onto them.

Step 6: Install the Return Line

The lift pump will also require a return line to send unused fuel back to the tank. Slice the fuel filler neck hose and splice in a tee fitting for the return line. Connect the return line to the tee fitting and route it back to the fuel tank. Ensure that all fuel lines are securely connected and free of leaks.

Step 7: Electrical Connections

Connect the electrical wiring harness to the lift pump, following the instructions provided with your kit. Typically, this will involve connecting the harness to the battery and fuse block, mounting the relay, and routing the wires to the pump. Be sure to use the correct gauge of wire and fuse ratings as specified in the instructions.

Step 8: Test the Installation

Once the lift pump is installed and all connections are secure, it's time to test it. Prime the pump and check for leaks. Turn the ignition to the "On" position and listen for the lift pump to engage. You may need to leave the new fuel filter loose with a pan underneath to catch any spilled fuel during priming. Attempt to start the engine and ensure that it fires up instantly. If the engine starts and runs smoothly, your lift pump installation is complete!

Step 9: Post-Installation Checks

After installing the lift pump, it's important to monitor your Duramax's performance and fuel system. Keep an eye on your fuel filter and change it at recommended intervals, especially if you've added additional filtration with the lift pump kit. Regularly inspect the fuel lines and connections for any signs of leaks. Additionally, consider using a fuel additive to enhance fuel quality and protect your injectors.

Pump the primer button

To bleed the fuel lines after a filter change on an LLY Duramax, you'll need to locate the primer button and the bleeder screw. The primer button is a big round metal cylinder on top of the housing, while the bleeder screw is a black screw with a small hole in it located towards the engine from the primer button.

To start the bleeding process, open the bleeder screw with a screwdriver and pump the primer button a few times. You'll see a stream of fuel coming out. If there are any squirts, burps, or interruptions in the stream, it indicates the presence of air in the fuel lines. Keep pumping until you achieve a full pump of diesel with no air bubbles.

Once you've ensured a consistent flow of fuel, close the bleeder screw and attempt to start the truck. If the engine starts and maintains its prime, the bleeding process is successful. However, if the engine loses prime and the issues persist, there might be other factors or leaks to address.

In some cases, you may need to repeat the process of pumping the primer button and cranking the engine multiple times before achieving a successful start. It is recommended to have a helper assist with cranking the engine while you focus on pumping the primer button. Additionally, having a jumper battery or a battery charger connected during this process can be beneficial.

Open the bleeder screw

To open the bleeder screw, you will need to locate it first. The bleeder screw is typically located on the filter assembly, towards the engine, and is a black screw with a small hole in the top. Once you have located it, use a screwdriver to open it up. Be careful not to overtighten the screw, as it is usually plastic and sealed with an O-ring. You only need to tighten it until it is snug, slightly more than finger-tight.

Once the bleeder screw is open, you can start pumping the metal primer button or plunger on the filter housing. You may need to pump several times or for an extended period to prime the fuel system and remove any air in the lines. You will know you have successfully bled the fuel system when a steady stream of fuel, without any squirts or burps, comes out of the bleeder screw. If you have an air compressor, you can speed up this process by applying low pressure air (2-5 PSI) to the fuel filler while keeping the bleeder screw open.

After bleeding the system, close the bleeder screw and continue pumping the primer button until it becomes hard to press. Then, try to start the engine. If the engine starts and then stalls, simply pump the primer button again until it is hard to press, without opening the bleeder screw. If the engine continues to stall after several attempts, it may indicate a leak in the system that is allowing air to enter.

In some cases, you may need to repeat the process of opening the bleeder screw, pumping the primer button, and closing the screw multiple times before the engine starts successfully. It is also recommended to crank the engine while priming to facilitate the process. Additionally, having a jumper battery hooked up while cranking can be helpful.

Close the bleeder screw and start the truck

Once you have completed the previous steps of bleeding your fuel lines, you can close the bleeder screw and start the truck. If your truck starts then stalls, you don't need to reopen the bleeder screw; simply pump the primer button until it is hard again and try to start the truck. If your truck continues to stall after a few cycles of this, then you may have a leak that is letting air into the system.

If you have an air compressor, you can apply low pressure air (2-5 PSI) to the fuel filler to save yourself some time and effort. Leave the bleeder screw open until fuel is present, then close it and try to start the truck.

If your truck starts and runs, you can take it for a drive. However, if you encounter the same issues that led you to change the fuel filter in the first place, you may need to rebuild the fuel filter housing.

Frequently asked questions