Replacing The Fuel Pump In Your Classic 1979 Mercedes 450Sl

If you're looking to replace the fuel pump on your 1979 Mercedes 450SL, you'll first need to locate it. The fuel pump is situated under the car on the right side, below the fuel-filling inlet near the fuel tank. You'll need to jack up the car and place it on jack stands to access the pump—be sure to wear safety glasses to protect your eyes from dirt and rust particles. Before starting work, disconnect the negative terminal on the battery and ensure the area is well-ventilated to minimise the risk of fire. Once you've located the fuel pump, you'll need to remove the plastic protective shield and the clamp securing the pump. You'll also need to disconnect the electrical terminals and the fuel delivery system. It's important to have rags and a fire extinguisher on hand in case of fuel leaks. When reassembling, ensure the new fuel pump's protective sleeve is centred in the mounting bracket to prevent corrosion.

The fuel pump is located under the car on the right side, below the fuel-filling inlet near the fuel tank

To change the fuel pump on your 1979 Mercedes 450SL, you'll first need to locate it. The fuel pump is situated under the car on the right-hand side, below the fuel-filling inlet, near the fuel tank.

Once you've located the fuel pump, you'll need to gather the necessary tools and parts. According to a guide for changing the fuel pump on a 1975-1980 450SL, you'll need an 8mm, 10mm, and 13mm socket wrench with a 6-inch extension, a 7mm, 8mm, and 17mm open-end wrench, a flat-face and Phillips-head screwdriver, a floor jack, and jack stands. You'll also want to have rags, a fire extinguisher, and a container to catch any spilled fuel on hand.

Before beginning any work, it's important to take safety precautions. Disconnect the negative terminal on the battery, and ensure the work area is well-ventilated. The guide also recommends consulting an article on safely jacking up your vehicle and placing it on jack stands. It's crucial to wear safety glasses when working under your car, as you don't want rust and dirt particles from the undercarriage to get into your eyes.

Now, let's go through the process of removing the old fuel pump, as outlined in the guide for the 1975-1980 450SL. Keep in mind that the steps may vary slightly for your 1979 model, and it's always best to refer to a vehicle-specific repair manual for exact instructions.

Removal Process:

• Using a 13mm socket, loosen and remove the two bolts holding the plastic protective shield.
• With an 8mm socket, loosen and remove the two nuts securing the clamp for the fuel pump.
• Use a flat-face screwdriver to loosen the clamp that feeds the fuel pump. If the fuel line is not clamped, place a receptacle to catch any fuel in the lines.
• Loosen and remove the two nuts securing the electrical terminals on the fuel pump using an 8mm open-end wrench.
• Loosen and remove the nut at the rear of the fuel pump, which secures the fuel delivery system, with a 10mm socket.
• Repeat step 5 for the nut at the front of the fuel pump.
• With a 17mm open-end wrench, loosen and remove the fuel line from the rear of the fuel pump. Ensure a proper fuel receptacle is in place to catch any leaking fuel.
• Loosen the hose clamp that secures the fuel suction dampener with a flat-face screwdriver. Again, make sure a fuel receptacle is in place to catch any fuel that may leak.
• The fuel delivery system can now be removed. Loosen and remove the fuel line feeding the fuel pump with a 17mm open-end wrench.
• At this point, the fuel pump is free to be replaced.

Installation Process:

As mentioned in the guide, the installation process is essentially the reverse of the removal process. Here are the steps outlined:

• Install the new fuel pump, ensuring that the protective sleeve is centered in the mounting bracket's clamp to prevent corrosion.
• Reattach the fuel line to the fuel pump using a 17mm open-end wrench.
• Secure the hose clamp for the fuel suction dampener with a flat-face screwdriver.
• Reconnect the fuel delivery system by securing the front and rear nuts with a 10mm socket.
• Reattach the electrical terminals to the fuel pump and secure them with an 8mm open-end wrench.
• Tighten the clamp for the fuel pump using an 8mm socket.
• Reinstall the plastic protective shield using a 13mm socket to secure the bolts.

Remember to always refer to a reliable vehicle-specific repair manual for the most accurate and up-to-date instructions on changing the fuel pump on your 1979 Mercedes 450SL.

Disconnect the negative terminal on the battery prior to any work

When working on a car, it is important to disconnect the negative battery terminal before starting any work. This is a safety precaution that can help prevent accidents and potential damage to the vehicle's electrical system. Here are several reasons why disconnecting the negative terminal is crucial:

Preventing Short Circuits: The negative battery terminal is connected to the vehicle's engine, body, and chassis. If you disconnect the negative terminal first, you eliminate the risk of accidentally creating a short circuit. This is especially important when working in tight spaces with a lot of metal surrounding the battery, as in the case of a 1979 Mercedes 450SL.

Safety: Disconnecting the negative terminal reduces the risk of electrical shocks or sparks when working on the vehicle. This is because the negative terminal is grounded to the chassis, and removing it first ensures that there is no path for current to flow through the chassis or engine block.

Preventing Damage to Electronics: Modern vehicles have sensitive electronic components and control modules. Disconnecting the negative terminal ensures that these components are not accidentally activated or damaged during repairs, preventing costly repairs or replacements.

Ease of Work: Disconnecting the negative terminal makes it safer and easier to work on the vehicle. You don't have to worry about accidentally touching a tool to the engine or chassis and creating a short circuit. This gives you more freedom to focus on the task at hand without constant worry.

Battery Maintenance: When conducting battery maintenance or replacement, disconnecting the negative terminal first is crucial. It helps prevent sparks and potential explosions caused by escaping battery gases. By following this step, you enhance your safety and protect the vehicle's electrical system.

Remember, when working on a 1979 Mercedes 450SL or any other vehicle, always put safety first. Disconnecting the negative battery terminal is a simple yet essential step to ensure a safer and more efficient repair or maintenance process.

Make sure the work area is well-ventilated

When working on your 1979 Mercedes 450SL, it is important to ensure that the work area is well-ventilated. This is crucial for your health and safety, as proper ventilation can help reduce the risk of inhaling harmful fumes and gases that may be released during the fuel pump replacement process.

Working on a car's fuel system can expose you to gasoline vapors and exhaust gases, which can be dangerous if inhaled in enclosed spaces. Gasoline vapors are highly flammable and can cause explosions if not properly ventilated. Additionally, exhaust gases contain carbon monoxide, a colorless and odorless gas that can be deadly if inhaled in high concentrations.

To ensure adequate ventilation, it is recommended to work in an open or outdoor space if possible. If you are working in a garage, make sure the garage door is open, and consider using fans to improve air circulation. If working in an enclosed space is unavoidable, wear a respirator or ventilation mask to protect yourself from inhaling harmful fumes.

It is also important to avoid any sources of ignition when working with gasoline. This includes sparks, open flames, or any devices that may produce sparks, such as power tools or electrical appliances. Keep the work area clear of any flammable materials and have a fire extinguisher nearby in case of emergencies.

By following these ventilation and safety precautions, you can help ensure a safer and more comfortable environment for replacing the fuel pump on your 1979 Mercedes 450SL.

The fuel pump's job is to supply the engine with enough fuel to maintain pressure

The fuel pump in a car is a critical component of the injection system and/or carburetor, responsible for ensuring the car's fuel circulation. Its primary function is to pump fuel from the tank to the combustion chamber, where it is converted into energy to start the engine.

In the case of your 1979 Mercedes 450SL, the fuel pump is located behind the right rear wheel, mounted in a cluster with the fuel accumulator and the filter. While it is considered an easy job to replace, caution must be exercised to prevent a fuel spill. It is recommended to have fuel line clamps and a large catch bucket to minimise the risk of a spill. Additionally, consider changing old rubber fuel lines and the filter.

The fuel pump operates by drawing fuel from the tank through a pipe to the carburettor, either mechanically by the engine or electrically. In fuel-injected engines, the pump may be located inside the fuel tank, supplying fuel to the engine and pressurising it.

Maintaining the fuel pump is essential for optimal performance. This includes regular cleaning of the tank, periodic cleaning of the pump, and servicing the injector nozzle and filter.

By understanding the function and location of the fuel pump, as well as following the necessary maintenance procedures, you can ensure the fuel system in your 1979 Mercedes 450SL operates effectively and safely.

Potential for fire is a concern when working on fuel systems, so disconnect the battery's negative cable to minimise the possibility of sparks

Working on a fuel system always carries a risk of fire, so it's important to take precautions to minimise the possibility of sparks. Before starting any work on your 1979 Mercedes 450SL's fuel system, it is essential to disconnect the negative terminal of your car's battery. This simple step can prevent potential shocks and sparks that could lead to a fire. Additionally, always make sure to wear appropriate safety gear, including gloves and safety glasses, to protect yourself from any fuel splashes.

When working on the fuel system, it is crucial to locate the fuel pump and identify the correct tools required for the job. The fuel pump on a 1979 450SL is usually mounted behind the right rear wheel, in a cluster with the fuel filter. To access the pump, you may need to remove the whole cluster and work on it on a bench or another suitable surface. Before beginning any work, ensure you have the necessary tools, such as an adjustable wrench or socket set, a screwdriver, rags or towels, and any required replacement parts.

One method to relieve fuel pressure without starting the car is to disconnect the fuel lines from the pump to the injectors. This will allow the fuel to drain from the line, relieving pressure. However, this method is not recommended for vehicles with an electric fuel pump as it may cause damage. Another approach is to manually trigger the fuel pump relay by connecting a jumper wire from terminal 30 to 86 in the fuse box. This will activate the pump, and you should observe pressure buildup on your pressure gauge.

Remember to secure all connections and tighten hose clamps and connectors once you have finished working on the fuel system. Taking these precautions will help ensure your safety and minimise the risk of sparks when working on the fuel system of your 1979 Mercedes 450SL.

Frequently asked questions