Replacing The Fuel Pump In A 1998 Mercedes C230: Step-By-Step Guide

Changing the fuel pump on a 1998 Mercedes C230 is a complex process that requires a range of tools and parts. The fuel pump is located under the car, and accessing it involves removing the rear seat and an access panel. It is important to work in a well-ventilated area when replacing the fuel pump, as harmful fuel vapors will be present. The process involves disconnecting the negative battery cable, removing the fuel cap, and using an anti-static siphon hose to drain the fuel tank. It is also necessary to depressurise the system through the Schrader valve under the hood. Once the fuel pump is accessible, the old pump can be removed and the new one installed, taking care not to damage the fuel level unit. Finally, the electrical connection, supply line, and return line can be reconnected, and the rear seat reinstalled.

Locating the fuel pump

The fuel pump on a 1998 Mercedes C230 is located under the car. To access it, you can start by looking in the trunk, towards the front-right side. You will notice a wire that comes through the floor and the black plastic panel in the trunk. This wire has a two-pin rectangular connector, which you can follow to find the fuel pump. The fuel pump relay is a small, green relay that energizes briefly when the starter engages and then while the engine is running.

Alternatively, there is an access panel under the rear seat cushion that allows servicing of the fuel pump. First, make sure to disconnect the negative battery cable for safety. Then, remove the fuel cap and use an anti-static siphon hose to drain the fuel from the tank into an approved storage container. It is recommended to work in a well-ventilated area or outdoors, as fuel and fuel vapors are highly combustible.

Next, depressurize the system through the Schrader valve under the hood of the car. This is important to avoid spewing gas all over the interior when disconnecting the lines. Once depressurized, you can locate the access panel to the fuel pump on the right-hand side of the fuel tank. There will be six 8mm screws holding the panel in place, which you can remove and gently pry the panel up. Be careful not to clean off the small sticky gasket between the panel and the body of the car, as it helps reduce noise and vibration.

With the access panel removed, you will see the locating cover and ring seal on the pump. There is a small arrow on the locating cover that aligns with a mark on the tank when reinstalling the pump. This cover and ring seal hold the pump in place inside the tank. Use a large claw-type wrench to remove the ring seal, as attempting to unscrew it by tapping the plastic notches with a flat-head screwdriver can shear off the notches.

By following these steps, you can successfully locate the fuel pump on your 1998 Mercedes C230 and proceed with any necessary maintenance or repairs. Remember to work in a well-ventilated area and take the necessary precautions when dealing with fuel and electrical systems.

Removing the fuel pump

To remove the fuel pump from your 1998 Mercedes C230, you will first need to disconnect the negative battery cable.

Next, remove the fuel cap and slide an anti-static siphon hose down the fuel filler neck to pump out the fuel from the tank. This is an important safety precaution to avoid spilling fuel and creating a fire hazard.

Make sure to depressurise the fuel system through the Schrader valve under the hood of the car. If you skip this step, you will release pressurised gas when disconnecting the lines, which can be extremely dangerous.

Now, you can locate the fuel pump, which is on the right side of the fuel tank. To access it, you will need to remove the rear seat. There is an access panel underneath the rear seat cushion that will allow you to reach the pump.

With the seat removed, you will see the access panel held in place by six 8mm screws. Gently pry this panel up, being careful not to damage the small sticky gasket between the panel and the body of the car, which helps to reduce noise and vibration.

With the access panel removed, you will see the locating cover and ring seal on the pump. There is a small arrow on the locating cover that will line up with a mark on the tank when you reinstall the pump. This cover and ring seal hold the pump in place inside the tank.

Use a large claw-type wrench to remove the ring seal. It is on tight, so be careful not to shear off the plastic notches by tapping them with a flat-head screwdriver.

Remove the ring cover and the shaped seal. Note how the two female ends in the cover mate with the two male ends on the pump.

Now, carefully remove the pump from the tank, being cautious not to damage the fuel level unit attached to it.

With the pump out, you can disconnect the following by squeezing the appropriate release tabs: the electrical connection, supply line, and return line.

Installation of the new pump is the reverse of the removal process. Take extreme caution when working with fuel, as it is highly combustible.

Disconnecting the fuel pump

Firstly, work in a well-ventilated area, preferably outdoors. Disconnect the negative battery cable. Remove the fuel cap and use an anti-static siphon hose to drain the fuel from the tank into an approved storage container. Depressurize the system through the Schrader valve under the hood of the car.

Next, remove the rear seat to access the fuel pump. There is an access panel under the rear seat cushion. Once the seat is removed, you will see the access panel to the fuel pump on the right-hand side. Remove the screws holding the access panel in place and gently pry it up. Be careful not to damage the small sticky gasket between the panel and the body of the car, which helps reduce noise and vibration.

With the access panel removed, you will see the locating cover and ring seal on the pump. Use a large claw-type wrench to remove the ring seal. Grasp the pump and remove it from the tank, being careful not to damage the fuel level unit attached to it.

Now, you can disconnect the following from the pump: the electrical connection, supply line, and return line. Release these by squeezing the appropriate release tabs.

At this point, the fuel pump is successfully disconnected and ready for replacement. Remember to exercise extreme caution when working with fuel and follow all safety guidelines.

Installing the new fuel pump

Now that you have removed the old fuel pump, it's time to install the new one.

First, prepare the new level sending assembly by slipping on the new seal and using zip ties to secure the end of all the hoses together.

Next, install the new unit. Snake the group of hoses along the front of the tank to reach the other side. Be careful not to damage the new level sender arm.

The group of hoses from the level sending unit is the same one that connects to the fuel pump assembly. Position them as they were before you removed the old assembly, and then lock down the sending unit. Cut the zip tie off the hoses as well.

Align the hose for the level-sending assembly with the nipple on the top of the assembly. Then, press the assembly into the tank. Slip the new lock ring onto the assembly and install the clamp around it. Use a 7mm socket to tighten the clamp. Then install the hose onto the top of the level-sending unit.

Now, slide the bottom half of the fuel pump assembly into the tank and attach the hoses and electrical connections from the level-sending unit. Then, place the new pump seal onto the tank and install the top portion of the fuel pump assembly.

Connect the electrical connection to the top of the assembly and then place the two pins with springs into the spots in the bottom half of the assembly.

Press the top portion into the seal once the two halves of the assembly are appropriately aligned. Then install the new lock ring and clamp. Use a 7mm socket to tighten down the clamp.

Finally, reconnect all of the electrical connections on the tops of both assemblies and start the car. Turn the key to the ignition on position before starting the car. Listen to hear the fuel system priming and then check for any leaks. If no leaks are present, start the car and take it for a test drive.

Testing the new fuel pump

Electrical Test:

• Check the fuel pump fuse in the fuse box. Refer to your owner's manual to locate the fuse box and identify the fuse for the fuel pump. Inspect the fuse for any signs of failure, such as burning or breakage.
• If the fuse appears damaged, replace it with one of the appropriate amp rating. Do not install a fuse with a higher amp rating than necessary.
• If the new fuse blows again, this indicates a direct short, and you should take your car to a repair shop for further diagnosis.
• Check the voltage at the fuel pump itself. Refer to your vehicle's service manual to locate the correct testing point and procedure.
• Perform a drop test using a voltmeter to ensure the power wire shows full voltage, and the grounding wire is properly grounded.

Fuel Pressure Test:

• Check the fuel filter to eliminate it as a potential issue. Remove the filter and drain excess fuel. Use a rubber hose on the filter inlet and blow through it, checking for resistance. Inspect the screen for debris, and replace the filter if necessary.
• Obtain a fuel pressure gauge, which can be purchased or borrowed from auto shops.
• Hook up the pressure gauge to the fuel pump test fitting, typically located near the fuel injectors. Refer to your owner's manual for the specific location.
• With the engine warmed up, have an assistant rev the engine while you check the pressure gauge. Check the pressure at idle speed and the rated speed specified in your pump specifications.
• If the needle on the gauge doesn't move or deviates significantly from the specifications, it indicates a problem with the fuel pump, and it may need to be replaced.

Additional Notes:

• Ensure you work in a well-ventilated area when testing and always keep a fire extinguisher nearby when working on the fuel system.
• If you are unsure about any part of the testing process, it is best to consult a professional mechanic or seek advice from a trusted auto repair forum.
• Refer to your vehicle's service manual or a repair guide specific to your car model for more detailed instructions and illustrations.

Frequently asked questions