Bad Fuel Filter Symptoms – How To Clean & Replace Fuel Filter?

Fuel filters are common in virtually all internal combustion engines. This important unit is responsible for filtering out unnecessary elements that go with the fuel, preventing them from infiltrating your car’s fuel system.

Otherwise, these particles can possibly damage some of your engine components.

Just like all automotive filters, the fuel filter can accumulate too much dirt, to the extent where it’s no longer able to strain out particles effectively.

It can even come to the point where it can already restrict the fuel flow.

This article will help you learn about the bad fuel filter symptoms along with how to clean and replace fuel filters.

Related: Top 3 Best Fuel Filter

Bad Fuel Filter Symptoms

There are a lot of tell-tale signs that indicate a faulty bad fuel filter. Usually, your vehicle alerts you with some symptoms.

1. Stalling

A fuel filter with already lots of amassed dirt can constrict the fuel flow to the engine. This restriction leads to a very unstable fuel supply.

As a result, you have a car that frequently stalls. For it to run efficiently and properly, your car requires a constant fuel supply.

Otherwise, it will simply stall. If this occurs frequently, it is quite likely your car has a dirty fuel filter.

2. Engine That Hesitates

A normal engine does NOT hesitate – it runs properly and as expected. You are likely to have a clogged, dirty fuel filter if your engine keeps hesitating when you press the accelerator.

This condition is attributed as abnormal combustion.

The clog restricts the flow of gas to the engine. It ultimately leads down to the state where your car has less responsiveness and reduced power.

So, another indication of a dirty fuel filter is when your vehicle stumbles while increasing speed, or when it simply doesn’t respond when you attempt to accelerate.

3. You Car Hard Starting

When you have a difficult time starting your engine, it’s more likely the fuel filter to blame again.

There are cases where your fuel filter has already gathered impurities but the volume is not enough to clog the passageway. If that’s the case, you will have a hard starting.

This condition means the fuel supply to your engine becomes quite limited, giving insufficient catalysts for proper combustion, thus making it harder to kick start the engine.

While a dirty fuel filter may cause some hard time starting, there can also be other potential factors behind.

This can include a bad carburetor or spark plugs. However, having your fuel filter replaced is a wise first step in diagnosing the problem.

4. You Car Not Starting

Just when you think nothing could be worse than hard starting; another symptom of a failing fuel filter is not being able to start the engine at all.

The combustion process will require an air-fuel mixture for it to initiate. However, the process can’t be done if there is no gas to enter the equation in the first place. 

Failure to start your engine means a high possibility your fuel filter is ‘completely’ clogged. 

This condition means you really have to replace the faulty fuel filter before you can start your engine again.

While a totally clogged fuel filter could cause a failed engine ignition, there are also other problems that share the same symptoms.

These include a deteriorating ignition or a dead battery. If you’re quite sure that you have a well-functioning battery and ignition, then you can fairly diagnose a bad fuel filter.

5. Problems at Lower Speeds

There are times you won’t be able to recognize the symptoms yet especially in the early stages of dirt build-up.

Even if your fuel filter is dirty, you can still run your vehicle particularly if the pressure is high. At high speeds, the fuel will still reach the engine, making your car operate just as expected. 

Higher speeds give your engine the ideal conditions for it to run efficiently. That is why the signs won’t rise at these moments.

However, the symptoms will start to show up when you run at slower speeds when the pressure are also declining proportionally.

At lower speeds, the fuel is not pushed to their destination as powerfully at higher speeds. This is where the engine starts to run rough or idle. You will also experience a hesitant engine. Worse cases include a power cut-out.

Further, there are high chances your vehicle will experience sputtering issues while driving at low speeds.

This may infer a minimal issue at the moment. But eventually, when the dirt volume gets worse, you will have no choice but to clean or replace the fuel filter. 

6. Check Engine Light Activates

Your vehicle’s way of telling you that something is not right is when the check engine light comes on.

All newer vehicles are equipped with fuel pressure sensors that keeps a continuous record of the fuel system’s pressure level.

The sensors can detect an abnormally low pressure phenomenon, triggering the check engine to turn on and alerting you of the issue.

While the check engine light is a big help in knowing there is something wrong, the light can also turn on due to a variety of other issues.

To confirm that it is indeed a bad fuel filter, you must have your car’s computer scanned for trouble codes.

You also may be interested in: How To Reset Check Engine Light

7. Foul Exhaust Odor

There are also cases where you can smell an awful exhaust fume odor. This symptom can possibly indicate a very unclean, clogged fuel filter.

The exhaust fume will come out in the form of dark, cloudy smoke.

If your car frequently misfires and emits a dark exhaust with a foul odor, you may want to check the fuel filter immediately.

When you have diagnosed a bad fuel filter, it’s a good step to have a professional mechanic inspect your car. The pros can assess whether it’s time to replace the fuel filter or not.

You also may be interested in: White Smoke From Exhaust – Causes & How To Fix

How To Clean Fuel Filters

While most fuel filters are relatively inexpensive to replace, a lot of car owners would still want to make the most out of it.

For instance, instead of directly replacing the fuel filter, they try to clean the unit first and get rid of the clog and dirt debris.

Cleaning is highly advisable if there is no actual damage to the component itself. That way, you can save or spend the money on something else.

Before starting, make sure you have these materials first:

  • B-12 Chem tool spray
  • Safety Glasses
  • Gloves
  • Jar or a basin
  • Flat-head screwdriver
  • Hose clamps

Related: Best Mechanics Tool Set

Here are the steps in cleaning fuel filters:

  1. For your own safety, always wear the safety glasses and gloves throughout the entire operation.
  2. Find the fuel filter. Start at the fuel line that comes into your carburetor or fuel injector. From there you can trace the fuel line to locate the fuel filter. It is placed along the line and appears to be a small plastic or metal canister.
  3. Close the hose on both ends with hose clamps to keep the gasoline from spurting. How to do this – on both the entrance and exit hose, screw hose clamps onto the fuel line. It must be 4 inches away from the filter. Grab a flat-head screwdriver and tighten the hose clamps as far as you can go.
  4. Take note of the arrow on the side part of the fuel filter. This points towards the engine. Take a picture or keep in mind the orientation because later, it’s important you re-attach the fuel filter on the same position.
  5. Now get the jar and place it under the fuel filter.
  6. Start unscrewing the hose clamps that link the filter to the hose. Note that this doesn’t pertain to the same hose clamps you used to secure the fuel line.
  7. Pull the hose away from the filter while you loosen the clamps simultaneously. The excess fuel will drip into the jar.
  8. Once the filter is released from the hoses, try emptying any residue left inside the filter into the same jar.
  9. Hold the filter in such a way one end directs into the jar.
  10. Now grab your B-12 Chem Tool. It has a small red straw that comes with it. Attach that straw to the spray nozzle. Now insert the other end to the fuel filter.
  11. Start spraying. You should see impurities drip into the jar.
  12. After spraying on one end, spray again on the other end.
  13. Try tapping the fuel filter against a hard surface, but gently. You can also tap the filter using the handle of the screwdriver. Continue tapping the entire surface of the fuel filter until most of the dirt are expelled out.
  14. Now get the B-12 Chem Tool again and blast the filter for another round. Spray on both ends.
  15. Set your fuel filter on a level surface and let it dry naturally for about an hour.
  16. After drying, you can now re-install the fuel filter back to the fuel lines.
  17. Reattach the filter and ensure the flow arrow is directed towards the engine. 

Note: Safety first. Be reminded again that’s important to wear safety glasses and gloves, especially the former.

Doing so will protect you against potential gasoline spray. A gasoline contact on eyes needs immediate medical attention. For skin contact, wash your skin right away.

How To Replace Fuel Filter

If you your vehicle is fuel-injected, changing the filter can be tricky. Replacing the fuel filter of fuel-injected cars requires you to disable the fuel pump first.

The fuel line may be secured to the filter with threaded fittings, clamps, or special fast-connect fittings.

  • You’re lucky if your fuel line only has clamps – they are relatively easy to disengage.
  • Special tools are required to disconnect special fast-connect fittings.
  • While a special flare-nut line wrench is needed for lines with threaded fittings.

Note: If changing your fuel filter requires you to buy necessary special tools, it’s probably more practical to have an auto mechanic do the job, especially if the said task is not done often.

Step 1 – Getting prepared

The first thing you need to do is to, of course, buy a new fuel filter. You can go to a local auto parts store and inquire for the right fuel filter for your make and model.

You should also ask whether there’s more than one needed. However, you can check your manual first to figure things out on your own.

Step 2 – Find the fuel filter

Your manual, again, can show you where the fuel filter is. If it doesn’t, you can ask a technician in your local dealership. If you don’t have a manual, a local library might cater your reference needs.

A fuel-injected engine has its fuel filter either under the hood along the fuel line close to the engine, or under the vehicle itself close to the fuel tank. Either way, it can be found somewhere in the high-pressure line.

Note: Let a professional deal with the replacement if a filter screen is inside the fuel tank while the fuel filter is in the fuel pump. An expert can handle if they get blocked up.

Step 3 – Relieve the pressure

Before disconnecting the fuel filter, DEPRESSURIZE the fuel line first by disabling the electric fuel pump. While the engine is off, get rid of the fuel pump fuse away from the fuse box.

Ensure your car is in Neutral or Park mode and that the parking brake is activated. Now turn ON the engine. You can’t expect the engine to last long but it would be enough to reduce the pressure in the fuel lines.

Now turn the engine off. You can now safely disconnect the fuel filter and the fuel line.

Step 4 – Compare the old and new filter

Make sure you have the right filter to replace before you fully remove the old one. You should also familiarize the orientation of the old filter. The new filter must be attached in the same orientation as the old.

Step 5 – Remove the old filter by taking away whatever is holding it in place.

Step 6 – Now attach the new filter in the same position as the preceding one.

Step 7 – Reinstall everything that holds the filter in place. Secure everything.

Step 8 – In the fuse box, replace the fuse for the fuel pump.

For this step, ensure your car is in Neutral or Park mode while the parking brake is on.

Step 9 – Test

You can now start the engine. Make some physical inspection whether there are leaks in the filter.

When To Replace Fuel Filter

Veteran mechanics and automotive share the same insight to replace fuel filter at least annually.

This is to make your car attain its optimum potential along with maximizing engine performance. Another fundamental rule is to change the fuel filter at least every 30,000 miles of usage. 

Vehicles that are often exposed to bumpy and coarse terrains should have their fuel filter replaced more often. The same thing is advised for a car that has already achieved a high mileage.

Replacing your fuel filter according to the right prescription will ensure that you have a smooth ride all the time, without having to worry of possible engine failure along the way.


There is really too much to discuss about fuel filters. It’s a good thing that you already know about the bad fuel filter symptoms along with how to clean and replace fuel filters.

Take your time to acquaint yourself with the fundaments of fuel filter. Surely, you can use the knowledge herein for future preferences. 

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