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

Changing the fuel pump on a Mercedes 126 can be a challenging task. It is important to follow the correct procedure to avoid any issues. The process involves removing the rear seat bottom covers, unscrewing the rear seats, and disconnecting the SRS cables. One must also be cautious when dealing with fuel lines and ensure that the gasket has a tight fit to prevent leaks. Additionally, it is recommended to use penetrating oil on bolts and fasteners for easier removal.

Disconnect the negative battery terminal

Disconnecting the negative battery terminal is one of the first steps to take when changing the fuel pump on a Mercedes 126. Here is a detailed, step-by-step guide on how to do this safely and effectively:

Step 1: Before beginning any work on your Mercedes 126, it is crucial to ensure your safety. Disconnecting the negative battery terminal will help prevent electrical shorts and reduce the risk of injury.

Step 2: Locate the negative battery terminal. It is usually marked with a "-" symbol or a black cover.

Step 3: Prepare your workspace by gathering the necessary tools, such as a wrench or socket that fits the battery terminal, and safety gear, including gloves and eye protection.

Step 4: Loosen the nut or bolt securing the negative battery cable to the terminal. You may need to use a wrench or socket to loosen it. Be careful not to strip the threads.

Step 5: Once the nut or bolt is loosened, carefully remove the cable from the terminal. You may need to wiggle it gently to detach it completely.

Step 6: After removing the cable, make sure to insulate the terminal to prevent accidental contact or arcing. You can use a piece of electrical tape or a terminal cover.

Step 7: Store the cable in a safe place away from the battery to avoid any accidental reconnection.

Step 8: If there is any corrosion or buildup on the terminal, clean it with a wire brush or a mixture of baking soda and water.

Step 9: Ensure that the area is clean and dry before proceeding with the fuel pump replacement or any other maintenance work.

Remember to follow all safety precautions and refer to a qualified mechanic or a detailed guide if you have any doubts about the process. Working with automotive batteries can be dangerous, so it is essential to take your time and prioritize your safety.

Remove rear seats

To remove the rear seats of a Mercedes 126, follow these steps:

First, remove the back seat bottom cushion. If you have power reclining rear seats, look for a bolt on each side of the bottom of the cushion. There is a washered nut on the back side that you can feel if the seat is pushed out far enough. Remove these bolts and push down on the front edge of the cushion while pulling it towards the front of the car. You may need to put your hands between the cushion and the seat back to pop it loose.

Now, for the backrest of the seat. If your rear seats are manual, there are three bolts that need to be removed: one on each side and one behind the armrest. Then, lift the seat back up and out of the metal slots by the parcel shelf.

If your rear seats are power-operated, run the seat all the way forward and undo the bolts at the floor at the rear of the seat frame. Do not try to unbolt the seat from the track. A universal joint on your socket may be needed to get the bolts out. Remove the cover from the seat belt track and remove the bolt, noting the orientation of the washer on the back so that you can replace it in the same way. Now that the rear bolts are out, run the seat all the way back and remove the plastic covers over the front bolts, then remove these bolts.

There is a carpet cover wrapped underneath the seat frame between the frame and the floor. Undo it to expose the plugs to the seat motor assembly. First, remove the two-pronged plug by squeezing the sides. Then, remove the three remaining plugs, starting with the large one first, carefully prying it up with a small screwdriver. Cut off the wire tie around the harness.

With the plugs removed, you or an assistant can now lift the seat out of the car. Lay it back slightly, then remove it through the rear door opening, remembering to slide the seatbelt track forward as it will get in the way.

Installation is the reverse of removal. Don't forget to plug the two-pronged plug back in before bolting the seat back in place.

Remove the fuel pump assembly cover

To remove the fuel pump assembly cover, you must first remove the rear seat bottom covers. There are no screws, just tabs. Releasing the tabs is the most challenging step, as they break easily. Once the covers are off, unscrew the rear seats. There are two hex nuts and several torx bolts. Disconnect the SRS cables—one for each seat.

Next, 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 you can work on 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.

Now you will see the top of the fuel pump. Take a picture to document the alignment of the pump connections.

Pinch off the fuel suction and delivery hoses

Pinching off the fuel suction and delivery hoses is an important step when changing the fuel pump on a Mercedes 126. This step ensures that you don't end up with a dangerous fuel leak and a potential fire hazard.

To start, make sure you have the right tools for the job. You'll need an appropriate clamping tool to pinch off the hoses. If you don't have a clamping tool, a pair of vise grips will also do the trick.

Now, locate the fuel suction and delivery hoses. These hoses are connected to the fuel pump, which is located at the bottom of the rear of the car. Once you've found the hoses, use your clamping tool or vise grips to pinch them off securely. This will prevent fuel from leaking out when you disconnect the hoses from the fuel pump.

It's important to note that when disconnecting fuel delivery lines, high-pressure fuel may be released. So, exercise extreme caution during this step. Always have a suitable container ready to catch any fuel that may spill. It's also a good idea to place towels around the work area to absorb any fuel that may leak. Remember to work in a well-ventilated area to minimize the inhalation of fuel vapors.

By following these instructions, you can safely pinch off the fuel suction and delivery hoses when changing the fuel pump on your Mercedes 126.

Disconnect the electrical wiring at the fuel pump

Disconnecting the electrical wiring at the fuel pump is a crucial step in changing the fuel pump on a Mercedes 126. Here is a detailed, step-by-step guide on how to safely and effectively complete this task:

Before beginning any work on your Mercedes 126, it is imperative to take necessary safety precautions. Ensure the engine is cool and wear protective gear, including gloves and eye protection. Working with fuel and electrical systems can be hazardous, so proceed with caution.

Step 1: Accessing the Fuel Pump

Locate the fuel pump, which is positioned beneath the rear passenger-side seat. To access it, carefully remove the rear seat flaps and bottom covers. There are no screws holding the covers in place, only tabs, so gently release them to avoid breakage. Once the covers are removed, unscrew the rear seats and disconnect the SRS cables for both seats.

Step 2: Preparing the Work Area

With the seats removed, you will have better access to the fuel pump. Slide the 60% seat (driver's side) towards the 40% seat (passenger side) to create more workspace. Fold the floor mat on the driver's side corner to expose the access hole for the fuel pump.

Step 3: Disconnecting the Electrical Wiring

Remove the seal and lift the cap covering the fuel pump. Take a picture or make a note of the alignment of the pump connections for future reference. Now, locate the electrical wiring (power line) connected to the fuel pump and carefully unplug it.

At this point, you have successfully disconnected the electrical wiring at the fuel pump. You can proceed with the next steps in the fuel pump replacement process, including disconnecting the fuel lines and removing the locking ring and the fuel pump itself. Remember to always follow manufacturer guidelines and seek professional advice if you are unsure about any part of the process.

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