Replacing Fuel Pump On Big Cam 400: Step-By-Step Guide

The Cummins Big Cam 400 is a powerful engine, but like any machine, it requires maintenance and occasional repairs. One such repair is replacing the fuel pump, which can be a complex task. The fuel pump is responsible for drawing diesel fuel from the tank and sending it to the injectors, where it is pressurized for injection into the engine. If the pump is not working optimally, it can cause issues such as hard starting and low power. In this guide, we will walk you through the process of replacing the fuel pump on a Cummins Big Cam 400 engine, covering topics such as accessing the pump, removing the old pump, and installing the new one. We will also discuss some common issues that may arise during the replacement process and provide troubleshooting tips to help you get your Big Cam 400 running smoothly again.

Removing the fender for easier access

Removing the fender will make the process of replacing the fuel pump on a Cummins Big Cam 400 engine much easier. The fender is held in place by six bolts, so removing it is a simple task.

Once the fender is removed, you will have much better access to the fuel pump, especially the pump's rear lower mounting bolt. In some cases, you may also need to remove the power steering pump to access this bolt. This is also a simple process and only requires the removal of two bolts.

With the fender and power steering pump out of the way, you will have a clear path to the fuel pump and can begin the process of replacing it. Remember to have the necessary tools and parts ready before starting the job, including a 12-point, 7/16 swivel socket for the upper rear mounting bolt.

Reinstalling the fender is just as easy as removing it. Simply line up the bolt holes and secure the fender with the six bolts. With the fender back in place, you can then move on to reinstalling the power steering pump if you had to remove it earlier.

Removing the power steering pump

To remove the power steering pump as part of the process of replacing the fuel pump on a big cam 400, follow these steps:

First, remove the fender, which should be a simple 6-bolt task. Then, to access the pump's rear lower mounting bolt, remove the power steering pump. This should be a simple 2-bolt removal.

The real trick to pulling the pump is the upper rear mounting bolt. For this, you will need a 12-point, 7/16 swivel socket, such as a Proto 5274. Once you have this, the rest of the task is very straightforward.

Using a 12-point, 7/16 swivel socket to remove the upper rear mounting bolt

To replace the fuel pump on a Big Cam 400 engine, you will need a 12-point, 7/16 swivel socket to remove the upper rear mounting bolt. This particular bolt can be tricky to access, so having the right tool is essential.

The 12-point, 7/16 swivel socket will allow you to reach the upper rear mounting bolt of the fuel pump. It is designed to fit onto the unique head of this bolt, ensuring a secure grip for removal. Attempting to use a different type of socket may result in rounding off the bolt head, making it even more challenging to remove.

When selecting a 12-point, 7/16 swivel socket, look for a quality product that can withstand the necessary torque without failing. Some reputable brands to consider include Proto and Matco. You may also find swivel sockets at hardware stores or automotive supply shops.

Once you have acquired the appropriate 12-point, 7/16 swivel socket, here is a step-by-step guide to removing the upper rear mounting bolt of the fuel pump:

• Locate the fuel pump: The fuel pump is typically located near the engine, often close to the fuel tank or fuel lines.
• Position the socket: Place the 12-point, 7/16 swivel socket onto the upper rear mounting bolt of the fuel pump. Ensure that the socket is securely engaged with the bolt head.
• Apply force: Using a ratchet or wrench, apply force to the socket in the counterclockwise direction to loosen the bolt. You may need to apply significant force, especially if the bolt is tight or rusted.
• Remove the bolt: Once the bolt is sufficiently loosened, turn it counterclockwise by hand or with a suitable tool until it is completely removed from its threaded hole.
• Access the fuel pump: With the upper rear mounting bolt removed, you should now be able to access and remove the fuel pump for repair or replacement.

Remember to work carefully and wear appropriate safety gear when performing any engine maintenance or repairs.

Checking for air in the fuel system

Step 1: Check for Physical Signs of Air in the Fuel Line

Begin by popping the hood of your vehicle and inspecting the fuel line between the fuel filter and injection pump. If you notice air bubbles in the fuel line or a complete absence of fuel, it indicates the presence of air in the system. This issue can lead to starting problems and engine performance issues.

Step 2: Inspect Fuel Lines and Connections

Pinhole leaks in the low-pressure fuel lines from the tank to the pump can cause air to be drawn into the system. Carefully examine the condition of all fuel lines, paying close attention to the connections between rubber flexis and solid lines. Look for any signs of damage, cracks, or wear that could allow air to enter the system.

Step 3: Check Seals and Filters

In addition to the fuel lines, inspect the seals on the fuel filter and other components in the system. Seals that are worn out or not properly seated can allow air to enter the fuel system. If you notice any damaged or compromised seals, replace them with new ones to ensure a tight seal.

Step 4: Deal with Air in the System

If you have confirmed the presence of air in the fuel system, the next step is to address it. One method is to use a hand diesel primer pump to prime the line and remove air bubbles. This process involves manually pumping fuel through the system to displace the air. Make sure to have a catch container or rag handy to capture any spilled fuel.

Step 5: Relieve Fuel System Pressure

Before performing any work on the fuel system, it is crucial to relieve the fuel system pressure. This can be done by activating the Schrader valve on the fuel rail, similar to releasing pressure from a tire. Place a rag over the valve and press the valve stem with a screwdriver to release the pressure. Alternatively, you can remove the fuel pump fuse or relay to let the system run out of fuel.

Step 6: Regular Maintenance and Prevention

To prevent issues with air in the fuel system, regular maintenance is key. Ensure that you replace your fuel filter at the recommended intervals and inspect the fuel lines and connections for any signs of wear or damage. By staying proactive, you can minimize the chances of air entering your fuel system and causing performance issues.

Adjusting the throttle shaft

• Locate the throttle shaft: This is where the throttle linkage hooks on. It is visible in the second picture where the linkage connects to the shaft.
• Access the adjustment screw: In the first picture, the adjustment screw is located under the 4-bolt cover that is under the gear pump. Remove the plug at the end of the cover to access the screw.
• Adjust the idle: Using a small flat-head screwdriver, turn the screw clockwise to increase the idle rpm. Be patient as the clicks are light, and do not adjust with the engine running as fuel will drain from the pump when the plug is removed.
• Check the button size: To check how much room you have to upgrade, remove the entire cover and snap ring holding the spring pack. Hold pressure when removing the snap ring to release the spring behind it.
• Adjust the throttle shaft screw: As mentioned by one user, the throttle shaft screw can be adjusted to improve throttle response. Loosen the lock nut and turn the screw counter-clockwise about a turn and a half to increase throttle response.
• Test and adjust as needed: Take the truck for a drive and use a screwdriver to adjust the throttle shaft screw until the desired throttle response is achieved.

It is important to note that adjusting the throttle shaft screw can affect fuel pressure and engine performance. It is recommended to have a fuel pressure gauge installed to monitor any changes in fuel pressure during adjustments. Additionally, be cautious when making multiple adjustments at once without knowing the actual fuel pressure values.

Frequently asked questions