Replacing The Fuel Pump In Your 99 Ml320: Step-By-Step Guide

The fuel pump in a 1999 ML320 is located inside the vehicle's fuel tank. To replace it, you will need to disconnect the battery, remove an access panel above the tank in the passenger compartment, and then remove the pump. You will also need to remove the fuel pump supply and return hoses, EVAP system hoses, and electrical connections to the pump. It is important to note that working with the fuel system can be dangerous, and there is a risk of fire, so it is recommended to let a professional handle this job unless you are very experienced in auto repair.

Disconnect the battery

Disconnecting the battery is the first step when replacing the fuel pump in a 1999 Mercedes-Benz ML320. This is a crucial safety precaution to reduce the chance of a fire when working on fuel system repairs.

• Park your car on a level surface and engage the parking brake. This will ensure your car remains stationary while you work on it.
• Locate the battery. The battery in most Mercedes-Benz ML320 models is located in the engine compartment on the passenger side, near the firewall.
• Identify the negative (-) and positive (+) battery terminals. They are typically marked or color-coded, with the positive terminal often having a red cover.
• Loosen the nut on the negative battery terminal using a suitable wrench or socket. Do not allow the wrench to touch any other metal parts of the car, as this could result in a short circuit.
• Carefully remove the negative battery cable from the terminal. You may need to wiggle it gently to detach it completely. Set the cable aside, ensuring it does not touch any metal parts of the car.
• Repeat the process for the positive battery terminal. Remove the positive cable in the same manner, taking care not to let it touch any metal surfaces.
• With both cables disconnected, you have now safely disconnected the battery. It is good practice to insulate the terminals with tape or plastic covers to prevent accidental contact during the fuel pump replacement process.

Remember, working on a car's fuel system can be dangerous, especially when dealing with electrical components. Always take the necessary precautions to ensure your safety and that of those around you. If you are unsure about any part of the process, it is best to consult a qualified mechanic or seek professional assistance.

Remove the rear seats and plastic panels

To remove the rear seats and plastic panels of your 1998 ML320, first remove any plastic panels behind the rear seat. Then, move the back seat all the way forward. You can either cut the carpet under the seat or remove the rear seat entirely and move the carpet out of the way.

Under the carpet, you will see a round metal panel glued to the floor. If you don't want to cut the carpet, you can use a heat gun to heat up the glue around the panel and pull it up. Removing this panel will expose the fuel pump. Before removing the fuel pump cover, disconnect the electrical connector and the two fuel hoses by pushing them in and then pushing the release clips. Be careful with the release clips as they break easily.

Cut the carpet under the seat

To cut the carpet under the seat of a 1998 ML320, first remove any plastic panels behind the rear seat. Move the back seat all the way forward to access the carpet underneath. Pull the carpet up and cut the section of the carpet that is glued to the floor of the car.

If you don't want to cut the carpet, you can remove the rear seat, move the carpet out of the way, and use a heat gun to heat up the glue around the panel. Then, pull the panel up.

Remove the electrical connector and fuel hoses

To remove the electrical connector and fuel hoses from your 1998 ML320, you will first need to remove the plastic panels behind the rear seat. If your car does not have these panels, you will need to remove the rear seat. Next, move the back seat all the way forward and cut the carpet under the seat. Pull the carpet up and you will see a round panel that is glued to the floor.

If you do not want to cut the carpet, you can remove the rear seat, move the carpet out of the way, and use a heat gun to heat up the glue around the panel. Then, pull the panel up. Under this panel, you will find the fuel pump. To remove it, you will need a special Mercedes-Benz tool to take off the fuel pump cover.

Before removing the fuel pump cover, take off the electrical connector and the two fuel hoses. Push the hoses in and then push the release clips on the lines and pull them out. Be careful with these hoses, as the release clips break easily.

To avoid the risk of fire, it is recommended that you let a repair shop handle this job unless you are very experienced in auto repair.

Check for leaks

Once you have installed the new fuel pump, it is important to check for leaks.

Before you start the engine, make sure that the rubber gasket has a tight fit between the pump and the tank. Otherwise, it may cause a leak when the tank is full. Put the locking ring over the pump and draw a line with a pen to mark its initial position. Then, turn the locking ring clockwise for at least 360 degrees. If you have the specific MB tool to remove and install the locking ring, the specification is 65Nm. If you don't have the specific tool, make sure it is tight enough or turned one full turn. Otherwise, it may cause a leak when the tank is full.

After you have secured the locking ring, snap the fuel lines into place. Make sure to refer to the picture to confirm the feed line, which plugs into the centre. Plug in the power cable and start the engine.

Finally, use body sealant to seal the cap. Install everything in reverse order, and do not forget to connect the SRS cable. Use Loctite for the seat nuts and bolts (40 Nm).

After the repair is done, be on the lookout for fuel leaks or odors. If you see or smell gasoline, do not start or drive the car, and do not park inside your house or under a covered structure. Have the car towed to a shop for inspection and repair.

Frequently asked questions