Symptoms of a Bad or Failing Fuel Filter

Any fluid that we put into our car has to run through a mechanism that will remove any impurities or … Continued

Any fluid that we put into our car has to run through a mechanism that will remove any impurities or potential contaminants so that these substances or particles don’t end up where we don’t want them to. This is the principal function of a filter. That is why we have oil filters, transmission fluid filters, and even brake fluid filters. Perhaps one of the most important filters of all is your fuel filter. After all, you do not want any impurity or contaminant to get mixed in your fuel and end up in your engine’s combustion chamber. Knowing the signs and symptoms of a faulty or problematic fuel filter can help you make the correct action to have it fixed and obtain the best possible performance from your engine.

car fuel filter

A Look at a Typical Fuel Filter

Before we get into the nitty-gritty of a failing or bad fuel filter, it is important to have a clear understanding about what this component is and how it works. This will also give you an idea as to why a number of symptoms observed in your vehicle will almost always point to a problem in the fuel filter.

As the name suggests, the fuel filter is a device that removes or filters out impurities or any other particle found in your fuel so that they will not end up in the engine’s fuel injectors or combustion chamber. Fuel is delivered from your fuel tank to the engine where it is mixed with air before being ignited to create a controlled explosion.

The fuel filter, therefore, sits anywhere along your car’s fuel line between the fuel tank and your fuel injectors (or carburetor in older cars). However, most modern cars now have the filter integrated right inside the fuel tank somewhere near the port where fuel exits the tank and into the fuel line. Wherever it may be located, its function remains the same: to remove any debris, dirt, particle, or contaminant that may be present in your fuel before this is delivered to the engine.

The fuel pump draws fuel from the tank to the fuel injectors or the carburetor. It also forces fuel through the fuel filter so that anything that is larger than the fuel gets trapped inside the filter itself. Only fuel is allowed to pass through.

Unfortunately, fuel filters aren’t permanent fixtures. They are mostly made up of pleated porous material that can get clogged over time. This is especially true if the fuel you are putting into your tank is full of impurities or that there may be sediments that have formed in the tank and these can get washed away with the fuel because of the pulling action of the fuel pump. These debris or particles can accumulate on the fuel filter. It is this accumulation of debris or particles that can reduce the amount of fuel that can pass through the filter.

Think of it this way. Imagine your kitchen faucet that has a filter at the tip of the nozzle. If you have brand new filter you will notice the flow to be strong. Over time, as sediments in the filter form, you will notice the water flow to be substantially lower than before.

The same is true with the fuel filter. If it gets clogged, then the amount of fuel going to the engine will also be affected. This is the main reason why you will see the different symptoms of a failing or bad fuel filter. Of course, if the fuel filter is severely damaged, it will either allow debris to go with the fuel clogging your fuel injectors or the filter itself will be clogged.

Symptoms of a Problematic or Bad Fuel Filter

As mentioned above, the fuel filter in your car acts as a sieve to separate larger particles from the fuel. If this is somehow affected, then you will expect the following symptoms.

fuel

Fluctuating Power at Varying Loads

One of the easiest ways you can identify a problem with the fuel filter is when you’re driving and you notice a loss of power or response from your engine. For instance, when you driver at an incline such as driving up a hill or even going over a bridge, you may notice a significant drop in your engine power. This occurs because the increase in fuel demand cannot be adequately met by the supply coming from the tank simply because there is clogging in the fuel filter.

Under load, the engine will have to work as hard. When you go the hill or over a bridge, your engine will require more power to go against gravity and push your vehicle up. The engine will need more fuel to produce more power. Unfortunately, because your fuel filter is already clogged with debris or particles which severely reduce the amount of fuel flowing through it, there simply is not enough fuel for the engine to use.

Check Engine Light

While it is true that majority of automotive onboard diagnostic systems do not have sensors for directly monitoring the integrity or function of fuel filter, there is always a chance that a clogged fuel filter can trigger a Check Engine warning light on your instrument panel. This is almost always related to any diagnostic trouble code that can indicate lean fuel.

For example, the trouble code P0171 may be noted which usually indicates that the fuel system of the car is running weak. Another trouble code that is worth mentioning is P0174 which is closely related to the mass air flow sensor, but can also mean that the fuel mixture in the engine is too lean. While these may indicate a problem with either the oxygen sensor or even the mass air flow sensor, a most likely culprit that is often overlooked is a clogged or failing fuel filter.

In many instances, the car owner may think that he needs to replace or fix either the MAF sensor or the oxygen sensor when in fact he should be focusing on the fuel filter which is, technically, a lot easier and less expensive to fix.

Engine Misfire

It is possible for a clogged fuel filter to cause engine misfire especially when under heavy engine load. It is important to realize that a partially clogged fuel filter will not really cause significant engine misfires while the engine is idling. However, once the engine requires substantial fuel such as what happens when it needs to go uphill or is carrying a much heavier load over a rough and uneven terrain, then the problem of fuel filter restriction can be easily identified.

Engine cylinder misfires caused by problematic fuel filter are usually random and do not point to a problem in a single cylinder. There is a possibility that all cylinders will be misfiring because of the insufficient amount of fuel that passes through the filter especially under heavy load. That is why it is imperative that the engine misfire be correlated with other issues in the engine.

Engine Stalling

This is a lot similar to engine power fluctuations related to the severely reduced flow of fuel through the fuel filter and into the fuel injectors. The engine requires sufficient amounts of fuel for it to operate. If the clog or damage in the fuel filter is substantial, then necessary amount of fuel may no longer reach the engine.

Sure, you may still be able to crank your engine simply because there is still fuel remaining in the fuel line. But as the engine runs and start burning this fuel in the combustion chamber, the fuel can get substantially low that there isn’t enough left that is being pumped into the engine. Hence, the engine stalls.

Under normal driving conditions you may have a normally functioning filter, fully capable of allowing fuel to the engine. Unfortunately, as soon as you step on the gas, the engine stalls because the increased demand for fuel is simply not being met anymore.

two fuel filters

Engine Will Not Start

If your engine will not start even though your fuel gauge says you have a tank full of gas, there’s a possibility that your fuel filter is completely clogged. Of course, engine not starting can also be caused by other problems such as a bad starter, a problematic alternator, a dead battery, or even faulty spark plugs.

It is also possible that the fuel pump is already failing. As you know, the fuel pump is what draws fuel from the tank through the filter and into the engine. If this is failing, then your engine will definitely not start, too. If all other components are working, then you can suspect complete fuel filter failure as the culprit for the engine not starting. It is often best to look at it with due consideration along with the other symptoms that you may observe.

Like everything else in your car, the fuel filter definitely has its own lifespan. Unfortunately, certain factors can substantially shorten its service life and can lead to a host of problems. Knowing these symptoms of a problematic or failing fuel filter can indicate the need for replacement.

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Sources:

  1. How to Diagnose a Bad or Failing Fuel Filter? – YourMechanic
  2. How to Clean a Fuel Filter – wikiHow
  3. How to Change a Fuel Filter – howstuffworks