Replacing The Fuel Filter In A 1990 300E: Step-By-Step Guide

If you own a 1990 300E, it's important to know how to replace the fuel filter. The fuel filter is located under the vehicle, between the rear tires, or behind the rear right side seat. Before starting, make sure to safely lift and support your car and use eye and hand protection as you will be working with gasoline. You will also need a 19mm and 17mm wrench, a Philips head screwdriver, and hose line clamps. Start by removing the cover and locating the fuel filter. Place a large hose clamping tool on the input line to the fuel pump and the fuel out line from the filter to stop the flow of gas. Remember to always replace all the brass washers between the fittings and the filter. When installing the new filter, make sure it faces the right direction -- it should flow towards the engine. Tighten everything down and turn the engine on and then off. Check for leaks before reinstalling the cover.

Fuel filter location

The fuel filter in a 1990 300E is located under the vehicle between the rear tires in plain view. It is cylinder-shaped and smaller in size than an oil filter. It is found above a plastic cover plate under the car, below the right rear seat.

To access the fuel filter, you will need to safely lift and support your car. You will also need to use eye and hand protection, as you will be working around gasoline. There will be some spillage when you remove the filter, so be prepared to catch any spills and dispose of the waste according to the regulations in your area.

Tools required

You will need a range of tools to replace the fuel filter in a 1990 300E. The fuel filter is located under the vehicle, so you will need a jack and jack stands to access it safely.

• Safety glasses and gloves
• Jack and jack stands
• Wheel chocks
• Ratchet set (ratchet, sockets, and extensions)
• Repair manual or access to a repair database
• 19mm and 17mm wrenches
• Philips head screwdriver
• Hose line clamps
• Flathead screwdriver
• Needle-nose or hose clamp pliers
• Plastic container or drip pan (for collecting spilled fuel)
• Penetrating oil (optional, for loosening rusted fittings)
• Thread sealant (if required for your specific vehicle)
• Fire extinguisher

The fuel filter in your 1990 300E is likely secured to the fuel line with flare nuts. To undo these, you will need:

• Flare nut wrenches
• Fuel line disconnect tool

However, some vehicles use different methods to secure the fuel filter, so you may also need:

• Quick-connect fittings
• Banjo bolt fittings
• Hose clamps
• Vice grips

Safety precautions

Safety is paramount when replacing a fuel filter. Here are some detailed safety precautions to follow when performing this task on a 1990 300E:

Park in a Safe Area and Prepare

Park your car in a level, well-ventilated outdoor area, away from open flames or sparks. Ensure you have the necessary tools, including safety equipment, and that you understand the process. Refer to your vehicle manual for specific guidance on your model.

Depressurise the Fuel System

Open the fuel filler cap and loosen it until you hear the pressure escaping. Then, locate and remove the fuel pump fuse or relay in the fuse box, typically accessible from inside the car on the driver's side. Start the engine and pull out the fuse or relay; the engine should die shortly.

Disconnect the Battery

Open the hood and disconnect the negative terminal on your car battery to prevent accidental sparks that could ignite gas fumes. Ensure you do not smoke or work near any potential ignition sources during this process.

Locate and Examine the Fuel Filter

The fuel filter on a 1990 300E is located under the vehicle, between the rear tires. Before attempting any work, ensure you relieve the pressure in the fuel line to avoid fuel spraying out. Examine the fuel filter and note its position and orientation, as well as how the fuel line is attached, so you can install the new filter correctly.

Use Appropriate Safety Gear

Throughout the process, wear safety goggles and disposable nitrile gloves to protect your eyes and skin from exposure to gasoline. Keep a powder-type fire extinguisher nearby as an extra precaution.

By following these safety precautions, you can help ensure that you replace the fuel filter on your 1990 300E safely and effectively.

Removing the old filter

To remove the old fuel filter from your 1990 300E, begin by safely lifting and supporting your car. You will need to use eye and hand protection, as you will be working around gasoline. Be prepared to catch any spills and dispose of the waste according to the regulations in your area.

Locate the fuel filter behind the rear right side seat. Remove the four 10mm plastic screws and pull the cover down and out. Be careful, as all kinds of things can collect under the cover. With the cover off, you will see the fuel filter mounted beside the fuel pump. Place a large hose clamping tool on the input line to the fuel pump and the fuel outlet line from the filter to stop the flow of gas from the lines. Remember that the filter will still be full, so be prepared for some spillage. If you do not have the proper tool, you can try wrapping vice grips in a rag to pinch the line. Just be sure not to put the metal teeth against the rubber line.

Hold the filter with a 19mm wrench and use a 17mm wrench to unscrew the banjo bolt fitting. Then, unscrew the line out fitting from the filter. Remember to replace all the brass washers between the fittings and filter.

Finally, remove the two Philips head screws, lower the hanger down, and remove the old fuel filter.

Installing the new filter

To install the new fuel filter, follow the removal process in reverse. First, ensure that the new filter is facing the right direction. The filter is designed to flow in one direction (towards the engine), so make sure to locate the flow direction on the new filter and install it with the arrow pointing towards the engine.

Next, hang the filter and pump on the rubber isolator hangers. Check the rubber isolator hangers for any damage, such as cracks or rips, and replace them if necessary.

Then, tighten the banjo bolt fitting and the line out fitting using a 17mm wrench. Remember to replace all the brass washers between the fittings and the filter.

Finally, replace the cover by screwing in the four 10mm plastic screws. Turn the engine on and then off. The engine might stumble for a moment after starting as the air is removed from the lines. Inspect for leaks before reinstalling the cover.

Frequently asked questions