Replacing The Fuel Filter In Your Classic 1988 Mercedes

Changing the fuel filter on a 1988 Mercedes-Benz is a straightforward process. Most vehicles made by Mercedes-Benz have two types of fuel filters: a strainer located in the fuel tank and another in the main fuel line. Symptoms of a failing fuel filter include a lit Check Engine light, rougher starts than usual, engine lag, and a misfiring engine. To replace the fuel filter, you will need a drain pan, needle-nose pliers, safety glasses, a slot screwdriver, vehicle ramps (if the filter is mounted underneath), a garden hose, and a fire extinguisher. First, relieve fuel pressure by unplugging the fuse or relay. Then, locate the fuel filter between the tank and the engine, disconnect and remove it, and install the new one. Finally, replace the fuse or relay and turn on the ignition to check for leaks.

Locate the fuel filter

To locate the fuel filter in your 1988 Mercedes, you'll first need to safely lift and support your car. You can refer to the article on jacking up your Mercedes-Benz. Once the car is safely supported, you can begin the process of locating the fuel filter and preparing for its replacement.

The fuel filter in your 1988 Mercedes is located on the underside of the car, behind the rear driver-side seat. To access it, you will need to remove the plastic protective piece that covers the fuel filter, accumulator, and pumps. This plastic cover is secured by three 10mm plastic nuts. Remove these nuts carefully and set the plastic plate aside.

With the cover removed, you will now have access to the fuel assembly, which includes the fuel pump, accumulator, and fuel filter. The fuel filter is part of this assembly and is connected to the other components by various fittings and hoses.

Before proceeding with the removal and replacement of the fuel filter, it is recommended to loosen the fittings on the filter. There will be a banjo bracket on one side and a fitting on the other, both of which are 17mm. You can use two wrenches for this step, one to hold the filter and the other to turn the fitting.

Disconnect and remove the filter

To disconnect and remove the filter, you will need to safely lift and support your car. You can refer to the article on jacking up your Mercedes-Benz. Once the car is safely supported, remove the plastic protective piece covering the fuel filter, accumulator, and pumps. This is held in place by three 10mm plastic nuts. Remove these and place the plastic plate aside.

The fuel assembly is suspended by four rubber hangers, which you can replace while changing the filter. Just slip the old hangers off and replace them with new ones. It is a good idea to loosen the fittings on the filter before attempting to remove it from its support. There is a banjo bracket on one side and a fitting on the other; both are 17mm. Use two wrenches to remove the lines, one to hold the filter and the other to turn the fitting.

With the lines to the filter removed, undo the metal bracket that holds the pumps, filter, and accumulator to the hangers. There are three Phillips-head screws that hold the bracket in place. Remove these and lower the bracket enough to remove the fuel filter.

Put in the new filter

Now that you've relieved the fuel pressure and removed the old filter, it's time to install the new one.

First, if your new filter didn't come with a plastic cover, transfer the old one onto the new filter. Next, install the new filter according to the flow direction—the fittings are different, so the filter will only fit one way. Make sure to install the two brass washers between the banjo bolt and snug everything up.

Once everything is in place, turn the ignition on and check for leaks. If there are no leaks, turn off the ignition and reinstall the cover plate.

Replace the fuse or relay

To replace the fuse or relay in your 1988 Mercedes, follow these steps:

Firstly, locate the fuse box. Modern cars have multiple fuse/relay boxes, so check under the hood, inside the passenger compartment, and in the trunk. Once located, refer to the fuse diagram on the lid of the fuse box or in your owner's manual to identify the fuse or relay associated with the component that is not working.

If you are dealing with a fuse, look inside the fuse to see if the small strip of metal is broken, indicating a blown fuse. If the metal strip is intact, the fuse is likely not the problem. However, if the metal strip is broken, simply find a new fuse of the same colour and amperage and replace it in the correct slot.

If you are dealing with a relay, turn the key to the off position and remove the faulty relay by unplugging it by hand. Then, insert the new relay in the correct position, being careful to use only as much force as is needed as the automotive wiring and connectors can be delicate.

Finally, turn the key to the on position or start the vehicle to verify that the component is functioning properly. If the component works, replace any covers or panels you removed for access.

It is important to note that replacing a blown fuse may not be enough to fix an electrical problem in your car. Fuses are designed to blow when a faulty component is drawing too much electricity, so the replacement fuse may blow too if the underlying electrical issue is not addressed. If you continue to experience problems, consider consulting a professional technician to diagnose and address the issue.

Check for leaks

Once you have finished replacing the fuel filter in your 1988 Mercedes, it is important to check for leaks. Turn on the ignition and observe the fuel filter and its connections for any signs of leaking fuel. If you detect a leak, turn off the ignition and tighten the fittings on the filter. You can also try replacing the washers between the banjo bolt and the filter. After making adjustments, turn the ignition on again and re-check for leaks. If no leaks are detected, turn off the ignition and reinstall the cover plate.

Frequently asked questions