Replacing The Fuel Pump In Your 1992 Mercedes 300E: Step-By-Step Guide

If you're looking to replace the fuel pump in your 1992 Mercedes 300E, you'll first need to locate it. There are two fuel pumps in this model, and they are located on the underside of the car. One pump is behind the rear right seat, and the other is behind the rear cross-member to the right of the differential. You will need to safely lift and support your car, and it's important to use eye and skin protection as you will be working around gasoline. Make sure to disconnect the cable from the ground post on your battery. You can then follow the provided instructions and diagrams to remove and replace the fuel pumps.

The fuel pump relay is located behind the plastic cover behind the battery

To access the fuel pump relay on a 1992 Mercedes 300E, you'll first need to locate the plastic cover behind the battery. This cover will need to be removed to access the relay.

The plastic cover in question is located behind the battery, so you'll need to start by locating the battery and then carefully accessing the area behind it. Be sure to refer to your car's manual or seek advice from a qualified mechanic if you're unsure about any of these steps.

Once you've located the plastic cover, you'll need to remove it to access the fuel pump relay. This cover should be relatively easy to remove, but again, refer to a professional if you're unsure. With the cover removed, you should be able to see the fuel pump relay, which will look like one of the two relays pictured in the source material.

If you need to replace the fuel pump relay, be sure to get the correct one for your car, as they are not interchangeable and can be expensive. The relay should be easy to remove and replace, but always take care when working with any electrical components in your vehicle.

Additionally, if you remove the fuel pump relay, you can jumper pins 7 and 8 to get the fuel pumps to operate.

The relay is not interchangeable with the MAS relay

If you have a MAS relay with a knob on top, it must be replaced with the same type of relay. The knob releases the relay. Rotate it counterclockwise. The MAS relay is responsible for fuel pump activation and cut-out, as well as A/C compressor control. It also provides current for the 02 sensor heater, controls the air injection pump, checks the engine coolant temperature, controls the start valve, and compares the engine speed and AC compressor speed.

The MAS relay is not interchangeable with other relays because it is designed to perform multiple functions. The relay is located behind the plastic panel behind the battery.

The fuel pump is located on the underside of the car

The pump is located under a plastic cover mounted just behind the rear cross-member. You will need to unclip the plastic cover from the rubber hangers and remove it. With the cover removed, you can see the line from the tank into the pump and the banjo fitting for the line out. Use an 8mm wrench to remove the ground connection, and then a 7mm wrench for the power side. Place a large hose clamping tool on the input line to stop the flow of gas. If you do not have the proper tool, you can try wrapping vice grips in a rag to pinch the line. Just make sure that you do not put the metal teeth against the rubber line.

With the hose pinched off, remove the Philips head screw from the hose clamp and wiggle the line off the pump. Be prepared for any gas remaining in the line of the pump to spill out. Use a 17mm wrench to hold the pump and another 17mm wrench to remove the bolt through the banjo fitting. Remove the fittings from the pump. Always replace the brass washers between the fittings on the lines.

There are two rubber hangers that hold the pump. Lift the pump up off the hangers and remove the rubber from the pump. Inspect the condition of the rubber hangers and replace them if needed.

One pump is behind the rear right side seat, the other is behind the rear cross-member

To access the fuel pump relay on your 1992 Mercedes 300E, you'll need to locate the plastic panel behind the battery. The relay will be behind this panel and will look like one of the two pictured relays.

Now, to access the fuel pumps themselves, you'll need to remove a plastic panel with a 10mm socket and a long extension. There are three screws that need to be removed before you can access the fuel pump/fuel filter area.

One pump is located behind the rear right-side seat, and the other is located behind the rear cross-member, just before the differential.

• Lift the rear seat cushion of the vehicle to access the fuel pump module, which is located behind the rear right-side seat.
• Disconnect the electrical connector from the fuel pump module and remove the fuel lines from the module.
• Remove the mounting bolts that secure the fuel pump module to the fuel tank and carefully lift it out.
• Install the new fuel pump module by securing it to the fuel tank with the mounting bolts.
• Connect the fuel lines and electrical connector to the new fuel pump module.
• Lower the rear seat cushion back into place.
• Repeat these steps for the fuel pump located behind the rear cross-member.

Please note that you will need to relieve the fuel system pressure and disconnect the negative battery cable before beginning any fuel pump replacement work. It is also highly recommended to have a certified mechanic perform these tasks to ensure safety and avoid any potential issues.

You will need to safely lift and support your car when changing the fuel pump

To change the fuel pump in your 1992 300E Mercedes, you will need to safely lift and support your car. You will be working around gasoline, so it is important to take the necessary safety precautions. Make sure to use eye and skin protection, and be prepared to catch any spills and dispose of the waste according to the regulations in your area.

• Jacking up your car: Refer to the article on jacking up your Mercedes-Benz W124. This will provide you with the specific steps and safety precautions for lifting your vehicle.
• Disconnect the battery: Locate the ground post on your battery and disconnect the cable. Ensure that the cable cannot accidentally come into contact with the terminal while you are working.
• Locating the fuel pumps: There are two fuel pumps in your Mercedes. The first pump is located on the underside of the car, behind the rear right side seat. The second pump is located behind the rear cross-member to the right of the differential.
• Containing spills: There will likely be some spillage when working on the fuel pumps, so be prepared with the proper containment equipment. Place a large hose clamping tool on the input line to stop the flow of gas. If you don't have this tool, you can try wrapping vice grips in a rag to pinch the line, being careful not to put the metal teeth against the rubber line.
• Removing the fuel pump: With the hose pinched off, remove the Phillips-head screw from the hose clamp and wiggle the line off the pump. Be prepared for any gas remaining in the line to spill out. Use a 17mm wrench to hold the pump and another 17mm wrench to remove the bolt through the banjo fitting. Remove the fittings from the pump and lift the pump up off the rubber hangers.
• Replacing the hangers: It is recommended to replace the rubber hangers while you are changing the fuel pump. Inspect the condition of the hangers and replace them if necessary.
• Reinstallation: Installation of the new fuel pump is the reverse of the removal process. Once everything is in place, turn on the ignition and check for leaks. Turn off the ignition and reinstall the cover plates.

Remember to work safely and follow all instructions carefully when lifting and supporting your car to change the fuel pump.

Frequently asked questions