Changing the fuel filter is part of routine vehicle maintenance and extends the life of the fuel pump. This element retains the residues present in the fuel, but over time it becomes clogged and its performance decreases; a blocked filter reduces the pressure and volume of gasoline in the fuel system. If the car loses power, the culprit could be a filter that is too dirty, so replace it respecting the frequency indicated by the manufacturer.
Note: This article only refers to gasoline vehicles. The filters of diesel cars and vans are usually larger, the entire fuel system is much more complex, as well as containing a large pressure (modern manifolds can produce more than 1000 bar of pressure); accidental release of this pressure could cause injury.
Steps
Part 1 of 3: Reduce the Pressure in the System
Step 1. Locate the fuse box
In order to reset the internal pressure of the fuel system you have to start the engine for a short time with the fuel pump not working and, to prevent this from doing its job, you have to find the fuse box in which there is what protects it. On most vehicles, the box is located in the passenger compartment or under the hood; consult the maintenance manual for specific information.
- If you don't have the manual, go to the car manufacturer's web page.
- The pump fuse is usually located in the box housed in the passenger compartment.
Step 2. Remove the fuel pump fuse
Once you have found the right box, use the diagram on the body of the box or in the manual to identify the fuse you are interested in and remove it with a pair of fine-tipped or plastic pliers.
- At this point the fuel pump cannot run when you start the engine.
- There is however some gasoline and pressure in the fuel lines running from the tank to the engine.
- If you don't have a fuse diagram, check the manufacturer's website.
Step 3. Make sure the shift lever is in the neutral position
Although the engine cannot get more gasoline from the tank, there is enough fuel in the system to start and run the vehicle for a while. If the car has an automatic gearbox, make sure it is in the parking position; if the car has a manual transmission, check that the lever is in neutral and that the parking brake is activated.
- Even if the car can only travel a few meters, if the gear is engaged it could move and pose a danger.
- If you are working on a vehicle with a standard transmission, check that the handbrake is on; if you have an automatic transmission, this precaution is optional, although highly recommended.
Step 4. Start the engine
Insert the key into the ignition and start the engine as usual. You shouldn't have any difficulties, as the engine is powered by residual fuel left in the system downstream of the pump.
- If the engine starts but then "dies", there may not be enough pressure for gasoline to reach it.
- If it goes out, the pressure inside the system is low enough to proceed.
Step 5. Let the engine run for one minute before turning it off
Depending on the system fitted to the vehicle and the average fuel consumption of the engine, the waiting time varies widely. However, there is no need to wait for the engine to turn itself off; let it run for a minute or two before removing the ignition key.
- With the pump off, the system's internal pressure should drop fairly quickly.
- If you let the engine stop by itself, you may have a hard time getting it started again later.
Step 6. Put the pump fuse back in place
Once the fuel system pressure has been reduced and the engine stopped, you can re-fit the fuse protecting the pump. Close the fuse box and restore all the items you had to take apart to get to it.
- Make sure the car is off before resetting the electrical contacts of the pump.
- Do not start the engine after replacing the fuse.
Part 2 of 3: Remove the Old Fuel Filter
Step 1. Disconnect the battery
At this point you no longer need to start the engine again until the end of the maintenance, you should therefore interrupt the electrical connection by removing the ground cable from the negative terminal of the battery; by doing so, you prevent the vehicle from accidentally starting while you work. Use a wrench or socket to loosen the negative pole nut, but don't unscrew it completely.
- This step ensures that the engine does not start during subsequent operations.
- Fit the negative cable between the battery and the bodywork to avoid accidentally restoring the electrical circuit.
Step 2. Locate the fuel filter
There are two housings in which it is usually mounted, so you must consult the manual of the machine you are repairing to know where to look. On modern cars, the most common location is the underbody, along the fuel system pipes, immediately after the pump; in other machines it is instead mounted in the engine compartment along the pipe that carries the fuel to the common manifold.
- In some models the filter is located in different points, always consult the maintenance manual.
- Sometimes, you need to access the cabin filter.
Step 3. Lift the machine if necessary
If the filter is placed in the underbody, you have to raise the vehicle to be able to reach it; insert the jack under the bodywork at one of the anchor points and rotate or push the crank to lift the car (depending on the jack model).
- Once the car is raised, insert safety jacks before sliding under the body.
- Don't rely solely on the jack to support the weight of the car as you work underneath it.
Step 4. Place a bowl or bucket under the fuel filter
Even if you have reduced the pressure inside the pipes, there may be some gasoline left in the system which could come out as soon as you remove the filter; therefore place a container under it to collect any liquid that drips and falls from the machine.
- Do not mix gasoline with oil or coolant to take to the recycling center; the fuel must be stored in a specific container until you can deliver it to the appropriate collection facility.
- Be careful with buckets or plastic bowls, gasoline could corrode certain materials and leak out of the container.
Step 5. Detach the clips securing the filter
Most of these items are locked in place with plastic hooks on either side of the cylinder that you can pry out of the holes with a flat screwdriver. Clips may break during this operation, so purchase replacement clips along with the new filter.
- The fixing hooks are made of thin plastic and tend to break easily; if you can remove them without breaking them, you can reuse them.
- You can buy the new clips at an auto parts store.
Step 6. Disconnect the fuel lines from the filter
Once the hooks are removed, pull the tubes away to detach them from the nozzle at the other end; remember to point them towards the bucket or bowl to collect the gasoline residues.
- You should wear safety glasses and gloves during this step to protect yourself from fuel splashes.
- Do your best to prevent the gas from falling to the ground.
Step 7. Slide the filter to detach it from the anchor brackets
It is likely to be held in place by a metal bracket that wraps around its outer body; once the hoses are detached, you can remove the filter by pushing it towards the front of the vehicle. This element should have a bell shape that allows you to move it only in one direction.
- If your model is stuck in the bracket in a different way, it may be necessary to push it towards the rear to take it apart.
- Some filters housed under the hood are attached to the bracket with a bolt that you have to unscrew.
Part 3 of 3: Install the New Fuel Filter
Step 1. Compare the replacement with the old part
Before mounting it, make sure it is the same as the previous one, that it has the same outside diameter, that the nozzles are identical, and that it can fit into the housing with the bracket.
- If the two are different, you need to go back to the shop and have the one you bought replaced with the correct model.
- Do not try to install an unsuitable filter, as it may not guarantee the passage of a sufficient volume of gasoline.
Step 2. Insert it into the bracket
The replacement should slide smoothly into the seat of the previous one; if you have to force it, it is likely to have the wrong diameter. The filter should also lock when properly mounted as it cannot slide fully in one direction.
- Be careful not to damage the external body, as this could cause leaks.
- If you find that you are pushing too hard to mount it, it is likely that it is not the right replacement.
Step 3. Connect the filter to the system
Insert the pipes into the front and back the same way they were connected to the old piece. Once the contacts are restored, secure the plastic clips in the holes in the fuel nozzle to lock the hoses to the filter.
- If the clips break during this operation, do not start the engine until you have replaced them.
- Make sure the hoses are snug on the nozzles before inserting the clips.
Step 4. Return the machine to the ground by removing it from the safety jacks
Lift it slowly, releasing the weight of the jacks and take the jacks out of the underbody. Lower the car by releasing the jack pressure or turning the crank counterclockwise, depending on the tool you have available.
- Make sure the jacks are out of the way, or you could damage the vehicle as you bring it back to the ground.
- Once it is grounded and safe, you can reconnect the battery to finish the job.
