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symptoms of a bad fuel filter

3 Symptoms of a Bad Fuel Filter You Should Not Ignore

by Gloria Louden
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Modern combustion engines can’t work without a decent fuel filter. Most people think that you can only find those in trucks or diesel cars, but that’s not the case. In fact, every vehicle has one of them tucked away somewhere, making it a bit of a challenge to get to if there are any issues.

And no issue should go ignored — in this article, we will cover three different symptoms of a bad fuel filter that any driver ought to look out for.

What Is a Fuel Filter?

Typically, a fuel filter is a component that works like most other filtration devices do. Its job is to make sure no debris reaches the engine while the car is running. Anything from dirt, dust and grime to various contaminants can wind up in the fuel tank and cause serious damage to the engine. And because of how porous it is, the filter will only allow clean fuel to go through.

Of course, like any other component, this filter will wear out over time. With constant use, an average fuel filter can get clogged up to the point where you can’t even start your car. That’s why it’s vital to think about replacement whenever you spot any of the symptoms of a bad filter we will list in this article.

How Do Fuel Filters Work?

Before we move on to the symptoms of a bad fuel filter and how to spot them, we need to take a look at how a functioning filter…well, functions.

Car manufacturers usually fit the filter somewhere along the vehicle’s fuel line. It can either be under the vehicle next to the fuel tank or inside the engine compartment. Some cars, like the 2010 Subaru Impreza, even have it inside the fuel tank itself. And while these models can last longer than regular filters, they also need changing once they start malfunctioning.

It’s important to note that not all filters are the same. For example, if you have a car with a  carbureted engine, it will use a metal or plastic filter with two tubes — an inlet tube on one end and an outlet tube on the other. A hose is attached over both ends using a circular clamp.

Then there are cars that use electronic fuel injection. Since these vehicles use a high-pressure fueling system, the fuel line has to be metal. These systems use fuel filters with a threaded fitting on each end. Moreover, you can easily screw the filter into the fuel lines.

Despite not being the same, however, most filters work in a similar fashion. When your car is running, the fuel pump “pushes” the fuel through the filter with the pressure it generates. Since all filters have sturdy, permeable materials on the inside, they only let the pure liquid through and keep all the grime away from the engine.

When Should I Change My Filter?

When it comes to engines in most cars, a regular fuel filter can work well for roughly 30,000 miles. Make sure to replace the filter as soon as you spot anything wrong with it after that mileage is run. The process might seem complicated, but most people with a basic knowledge of tools and mechanics can do it. Of course, we always recommend consulting an expert mechanic if you spot any symptoms of a bad fuel filter in your car.

Important Notes for DIY Fuel Filter Changes

  1. If the fuel tank is in the engine or underneath the car, you might be able to replace it yourself. However, don’t try to do it if the filter is inside the tank. Sometimes, these filters will not be serviceable and you will have to take the car to a professional mechanic.
  2. Fuel lines attached to the filter work under tremendous pressure. So, if you want to detach them, make sure to relieve some of that pressure first; one common way is to remove the control pump fuse and idle the vehicle until it runs out of gas.
  3. Pay attention to the connector types of your fuel lines. For instance, lots of old cars use a hose clamp connector, or even a nut and bolt. These connectors will hold, but they aren’t suited for a high-pressure engine. Most new cars use a special snap that anyone can disconnect easily.
  4. When taking the filter out, you might want to cut it open. Looking into the filter can let you determine what went wrong and help you deal with any future fuel filter issues.
  5. Priming the engine after the filter change is a good idea. You achieve this by “bleeding” the system of any air bubbles. There are cars that have manual pumps along the fuel lines, and by gripping them you pump the air out yourself. Of course, lots of modern cars have an automated air bleeding sequence that does all the work for you.

Which Filters Do I Get?

In case you decide on a DIY filter change, you’ll need to find the best products out there that will get the job done. Here’s a handy little list of top 10 best filters on the market today:

But What Happens if I Don’t Change It?

If left unchecked, the fuel filter will clog up and prevent any fuel from reaching the engine. If that happens, your car can experience a host of different problems.

You might hear a sputtering noise when your car accelerates. That’s the engine not receiving enough power to run properly due to not enough fuel reaching the tank. During this event, your check engine light might be turned on, and the car will continue at a sluggish pace. More importantly, it might stop altogether.

However, you can experience even more serious problems than a stuttering car or a blinking light on your dashboard. For instance, a worn filter can fail to trap a speck of dirt or a piece of debris. As a result, this foreign object will break down within the engine or the fuel lines and damage them internally. Moreover, the debris can clog the fuel injectors, which will only cause further damage to the engine and the fuel system.

The 3 Symptoms of a Bad Fuel Filter

Before moving on, we should stress that there is no surefire way of telling if your fuel filter is bad or not. In fact, most people will attribute the symptoms of a bad fuel filter to some other engine issue, and vice versa. In order to avoid disassembling the engine for no reason, we suggest you undertake the following steps:

  • Check your car’s service logs
  • Run a diagnostic and see if there are any errors
  • Check your spark plugs, fuel pump, and fuel lines for any damages
  • See if the battery is full in case your car isn’t starting

If none of the steps above produce any positive results, you can assume that the filter might be the problem based on the following symptoms.

Symptom #1: Random Misfiring

Did you ever hear your engine buck, jerk, or start off rough? Did this happen when you drove up a hill or under a heavy load? That’s probably because a random cylinder had misfired when you started the car.

Misfiring happens when the engine fails to go through one of the combustion process steps. Fuel is vital for this process to take place, so a clogged filter is the most likely culprit for this issue.

However, a clogged filter will not cause any misfires when your car is parked and idle. To be precise, the only time a filter might cause misfires in a stationary car is if the debris has completely clogged it. Otherwise, something else might be causing the problem.

Symptom #2: Engine Stalling

Engine stalling is another symptom of a clogged filter that you can check for by driving up a hill or a steep incline. Usually, a car with no immediate issues will have no trouble going up. However, pay close attention if the engine begins to stall when you attempt an incline drive.

Because of all the debris blocking the filter’s pores, the engine becomes starved of fuel since very little of it passes through the fuel lines. When that happens, it begins to stall or just outright stops. You won’t normally notice this on a straight road. However, when you try to drive up an incline, your car needs to accelerate, which means it needs more fuel than usual, and it might not be coming through because of a clogged filter.

Symptom #3: No Power in the Engine

When a filter is clogged, no fuel goes through and there’s no pressure in the engine. As a result, the car might fail to even start. The Engine Control Unit, or ECU, will restrict the engine’s output in case there’s not enough fuel reaching it. In other words, the whole system goes into “limp” mode and you can’t start the car.

A wide variety of cars out there have fuel pressure sensors. They are responsible for checking the amount of pressure within the fuel system and once they spot a significant drop, the check engine light switches on. A clogged filter is one of the reasons why the pressure might be dropping. However, this lamp also switches on if the car idles or if it fails to start at all.

A Few Final Words

There are other, minor symptoms of a bad fuel filter, but the fueling system is quite complex and, as you saw, any one symptom can point to an entirely different problem. However, should you spot a clogged filter, either try to replace it yourself or, if you don’t think you’re up for the task, get your vehicle to the nearest mechanic.

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