Replacing The Fuel Pump In Your Mercedes-Benz S550

Replacing the fuel pump in your Mercedes-Benz S550 can be a complex task and is best left to professionals due to the risk of fire. The fuel pump is responsible for delivering gas from the fuel tank to the fuel injectors, and issues with it can cause a loss of engine power or prevent the car from starting. The average cost for a Mercedes-Benz S550 fuel pump replacement is between $974 and $1,004, with labour costs estimated between $113 and $142, and parts typically priced around $861.

Disconnect the battery

Disconnecting the battery of your Mercedes-Benz S550 is a crucial first step when replacing the fuel pump. This step is important to reduce the chance of a fire occurring during the replacement process. Here is a detailed guide on how to safely disconnect the battery:

First, locate the battery. The battery is typically located in the engine bay of your S550. Open the hood of your vehicle and identify the battery, which is a rectangular unit with two terminals: a positive (+) terminal and a negative (-) terminal. The positive terminal will typically have a red cable attached, while the negative terminal will have a black cable.

Next, gather the necessary tools. You will need a wrench or socket set to loosen and tighten the battery terminals. It is also recommended to wear protective gear, such as gloves and eye protection, to safeguard against any potential battery acid spills. Place a mat or cardboard underneath the battery to catch any spills or debris.

Now, you are ready to begin the disconnection process. Start by loosening the negative terminal. Use your wrench or socket to loosen the nut or bolt holding the negative cable in place. Once it is loose, carefully remove the cable from the terminal. You may need to wiggle the cable gently to detach it completely. Set the cable aside, ensuring it does not touch any metal parts of the car to avoid creating a short circuit.

After the negative cable is disconnected, move on to the positive terminal. Again, use your wrench or socket to loosen the nut or bolt securing the positive cable. Remove the cable from the terminal and place it away from any metal surfaces.

With both cables now disconnected, you have successfully disconnected the battery. It is important to note that disconnecting the battery will result in a loss of power to various electronic systems in your vehicle, including the clock, radio, and navigation system. Therefore, it is advisable to have your radio code handy if your vehicle is equipped with an OEM (Mercedes-Benz supplied) radio. Additionally, some vehicles may require a reset of certain electronic settings after reconnecting the battery.

Remember to exercise caution and follow the correct sequence when disconnecting the battery. Always start with the negative terminal first and then move on to the positive terminal. This order is essential for safety reasons and to minimize the risk of electrical shorts or damage to sensitive electronic components.

Remove the access cover

To remove the access cover of your Mercedes-Benz S550's fuel pump, you will need to begin by removing the rear seat flaps and bottom covers. There are no screws, only tabs, so be careful not to break them when releasing the tabs. Next, unscrew the rear seats. There are two hex nuts and several torx bolts. Disconnect the SRS cables—one for each seat.

Now, remove the 40% seat (rear passenger side) from the car. The 60% seat is very heavy, so just slide it to the location of the 40% seat so that you can access the driver's side. Fold the floor mat (driver-side corner) and you will see a round cap covering the access hole. This cap is attached to the body by sealant only. Remove the seal and lift the cap.

You will need to use a utility knife to carefully remove the body sealer that covers the metal cover of the fuel pump. Go slowly and try not to get the knife stuck, as this could break off a small part of the cover.

Once the seal is removed, you will see the top of the fuel pump. Take a picture to document the alignment of the pump connections.

Replace the pump and pre-pump filter screen

To replace the pump and pre-pump filter screen of your Mercedes-Benz S550, you will need to follow a careful procedure to ensure your safety and the integrity of the vehicle. Here is a step-by-step guide:

Step 1: Disconnect the Battery

Before beginning any work on the fuel system, it is crucial to disconnect the battery to reduce the risk of fire. This is an essential safety precaution.

Step 2: Access the Fuel Pump

If the fuel pump is located inside the fuel tank, you will need to remove an access cover to reach it. In some cases, you may need to drain the fuel before removing this access panel. If the pump is outside the tank, proceed to the next step.

Step 3: Remove the Old Fuel Pump

If your S550 has the fuel pump located outside the fuel tank, disconnect the fuel lines and remove the old pump. This process may vary depending on your vehicle's specific configuration.

Step 4: Install the New Fuel Pump

Install the new fuel pump, ensuring that all connections are secure. If the pump is inside the fuel tank, you will need to access it through the opening and securely install it in place.

Step 5: Replace the Pre-Pump Filter Screen

Along with replacing the fuel pump, it is recommended to replace the pre-pump filter screen as well. This screen is located before the fuel pump in the fuel line and helps to filter out any contaminants before they reach the pump.

Step 6: Reassemble and Check for Leaks

Once the new fuel pump and filter screen are in place, reassemble any components that were removed to access the pump. Ensure that all connections are secure and properly tightened. Finally, check the fuel system for any leaks. Start the engine and inspect for any signs of fuel leaks. Ensure that the problem has been resolved and that the fuel pump is functioning correctly.

It is important to note that working with the fuel system can be dangerous due to the risk of fire. If you are not confident in your ability to perform this replacement, it is recommended to seek the services of a professional mechanic. Additionally, always take the necessary precautions when working with flammable liquids and ensure proper ventilation.

Check for leaks

When replacing the fuel pump on your Mercedes-Benz S550, it is crucial to check for leaks to ensure a safe and proper installation. Here are some detailed instructions and considerations to help you with this important task:

Before starting the replacement process, it is recommended to siphon as much fuel as possible from the tank to minimize the risk of spills during the procedure. While it is not necessary to completely drain the tank, having less fuel will make the process safer and more manageable.

After you have removed the old fuel pump and installed the new one, carefully inspect the area for any signs of fuel leaks. Pay close attention to the connections and hoses, as these are common sources of leaks. Look for any dripping or pooling fuel, and make sure to tighten any connections that appear loose.

If you notice a fuel leak, there are a few potential causes to investigate:

• Locking Ring or Rubber Seal: Ensure that the locking ring is tight and secure. Over time, vibration can cause the locking ring to loosen, leading to a leak. Additionally, check the rubber seal around the pump. It may have been damaged during the installation process or not seated correctly.
• Copper Washers: The copper washers used at fuel connection joints between hoses, pumps, and filters can harden over time and leak due to vibration. Replacing these washers is a simple and inexpensive solution that may resolve the issue.
• Fuel Lines: Inspect all fuel lines for cracks or damage. If a line is compromised, it may need to be replaced.
• Fuel Cap: Ensure that the fuel cap is tight and secure. A loose cap can cause fuel to leak, especially when the tank is full.

Remember, working with the fuel system can be dangerous due to the risk of fire. Take all necessary precautions, and if you notice any fuel leaks or odors, do not attempt to start or drive the car. Instead, have the vehicle towed to a repair shop for further inspection and repair.

By carefully checking for leaks and addressing any issues, you can help ensure the safe and proper functioning of your Mercedes-Benz S550's fuel system.

Test the fuel pressure

To test the fuel pressure on your Mercedes-Benz S550, you will need a fuel pressure gauge. The Actron CP7818 fuel tester is one option that works on most Mercedes-Benz and has the required Schrader valve.

• Open the hood of your Mercedes-Benz and remove the engine cover. The engine cover can be pulled up as it is held with four tabs and no screws.
• Locate the fuel test port on the fuel rail. If you cannot find the fuel pressure port (Schrader valve), start from one of the fuel injectors and follow the fuel rail.
• Remove the Schrader valve cap.
• Connect your fuel pressure tester.
• Turn the ignition on and check if the fuel pressure builds up before cranking the engine.
• Start the motor and get a fuel pressure reading. The recommended fuel pressure range with the vacuum hose disconnected is 54-61 PSI.
• Observe the fuel pressure at idle and when revving the engine. The fuel pressure should fluctuate slightly (+/-2 PSI) when revving the engine.
• Keep the RPMs constant at 4000, 2000, and idle, and observe the fuel pressure. It is a good sign if the fuel pressure doesn't change much.

If you find that the fuel pressure is low or nonexistent, the next step is to check the pump's electrical circuit. This may involve checking the voltage at the fuel pump and testing the fuel pump relay. If the pump is not receiving enough voltage, there may be a problem with the electrical connection or the Engine Control Unit.

Frequently asked questions