Replacing Fuel Pump In Mercedes 126: Step-By-Step Guide

Replacing the fuel pump on a Mercedes 126 can be a complex task. The fuel pump is located at the bottom rear of the car, and there are several steps involved in accessing and replacing it. First, the fuel tank filler cap must be removed to depressurize the fuel tank, and the negative battery terminal should be disconnected and insulated. The fuel pump assembly cover can then be removed, and the fuel suction and delivery hoses pinched off with an appropriate clamping tool or vice grips. The metal fuel line connecting the fuel accumulator, fuel filter, and fuel pump must be removed, and the fuel suction hose disconnected from the fuel pump. The electrical wiring at the fuel pump can then be disconnected, and the mounting screws on the fuel pump bracket loosened to remove the fuel pump. It is important to note the position of the fuel pump and insulating sleeve before removal. When reinstalling the new fuel pump, it is recommended to use new sealing rings when reconnecting metal fuel lines. Finally, the engine can be run to check for fuel leaks.

Disconnect the battery and fuel lines

Disconnecting the battery and fuel lines is an essential step when replacing the fuel pump on a Mercedes 126. Here is a detailed guide on how to do this safely and effectively:

Firstly, locate the negative terminal of your car battery. This is usually marked with a '-' symbol and connected to the battery with a black cable. Disconnect this terminal and insulate it to prevent any electrical short circuits during the fuel pump replacement process.

Now, let's turn our attention to the fuel lines. Place a drip pan or a large container under the fuel lines to catch any spilling fuel. The fuel lines are under pressure, so it is important to relieve this pressure before disconnecting the lines. To do this, open the gas cap to release the built-up pressure in the fuel tank.

Once the pressure is released, identify the fuel lines that connect to the fuel pump. There should be a metal fuel line and a rubber hose connecting the fuel pump to the fuel tank. Using a suitable wrench, loosen and disconnect the metal fuel line that connects the fuel accumulator, fuel filter, and fuel pump. Be cautious, as there may still be some residual fuel in the lines, and always keep a fire extinguisher nearby when working with flammable liquids.

After disconnecting the metal fuel line, focus on the rubber hose. Using your screwdriver, carefully loosen and remove the clamp that secures the rubber hose to the fuel pump. Slowly pull the hose away from the pump, being prepared for any remaining fuel to spill out.

At this point, both the metal fuel line and the rubber hose connecting the fuel pump should be disconnected. It is important to note that there may be slight variations in the fuel line configurations depending on the model year of your Mercedes 126. Some models may have two fuel pumps, so ensure you disconnect the correct fuel lines corresponding to the pump you are replacing.

Always refer to the manufacturer's instructions or a trusted repair manual for your specific Mercedes 126 model when performing fuel pump replacement. Working with fuel systems can be dangerous, so ensure you take the necessary precautions and have the appropriate tools and safety equipment before proceeding.

Remove the fuel pump assembly cover

To remove the fuel pump assembly cover on a Mercedes 126, first remove the fuel tank filler cap to depressurise the fuel tank. Disconnect the negative battery terminal and insulate it. You will then be able to remove the fuel pump assembly cover.

Use a clamping tool to pinch off the fuel suction and delivery hoses

To replace the fuel pump on a Mercedes 126, you will need to use an appropriate clamping tool to pinch off the fuel suction and delivery hoses. This is an important step as, without clamping the hose, fuel will continue to pour out of the tank.

You can use a pair of vise grips as a clamping tool. Place the clamping tool on the large line coming from the tank. Alternatively, you can drain the tank by opening the gas cap to relieve any built-up pressure.

It is important to note that when disconnecting fuel delivery lines, high-pressure fuel may be released. Therefore, ensure you take the necessary precautions to avoid any hazards.

Remove the metal fuel line connecting the fuel accumulator, fuel filter and fuel pump

To remove the metal fuel line connecting the fuel accumulator, fuel filter, and fuel pump, you will need to first relieve any built-up pressure in the gas tank by opening the gas cap. Next, use an appropriate clamping tool to pinch off the fuel suction and delivery hoses. When disconnecting the fuel delivery lines, be cautious as high-pressure fuel may be released.

Now, remove the metal fuel line. Pay attention to the wiring—one wire is positive, and the other is negative. A small wrench is useful for this step. If you are having trouble removing the wiring, you can skip this step for now and come back to it later.

Once the wiring is disconnected, slowly pull the hose away from the pump. There may be some resistance as it comes over the flange, and any leftover gas in the tank and hose will come flowing out rapidly.

If you were unable to disconnect the wiring earlier, you can try rotating the whole pump and metal pipe link to better reach. Be careful not to put too much slack on the wires.

After removing the metal fuel line, be sure to use new sealing rings when reconnecting it.

Reinstall the fuel pump(s) in reverse

To reinstall the fuel pumps in reverse, first, loosen the mounting screws on the fuel pump bracket. Next, insert the insulating sleeve(s) on the fuel pump(s). Now, reconnect the electrical wiring at the fuel pump(s). Be sure to note the position of the fuel pump(s) and insulating sleeve(s) before reinstallation. Then, reconnect the fuel pump connecting line between fuel pumps M3/1 and M3/2. Following this, reconnect the metal fuel line that connects the fuel accumulator, fuel filter, and fuel pump.

After this, reconnect the fuel suction hose to fuel pump M3/1. Be sure to use new sealing rings when reconnecting metal fuel lines. Finally, reinstall the fuel pump assembly cover and reconnect the positive battery terminal.

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