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Bad Fuel Filter Symptoms: Signs Your Fuel Filter is Clogged

For engine oil, coolant, and brake fluid, purity is important. But in no other system is clean fluid as important as the fuel system. Whether you drive a gas- or diesel-powered vehicle, contaminated fuel leads to a host of problem. A fuel filter is installed in every vehicle to remove the particles that could cause lasting damage to your engine if they got that far.  

A fuel filter is a maintenance item and needs to be replaced routinely. Failing to do so can cause troubles of its own that affect performance, reliability, and economy. When should you change the fuel filter, and what does it look like when the fuel filter is clogged? Here’s what you need to know about the symptoms and what you can do about it. 

What Does Your Fuel Filter Do?

No matter where it comes from, any gasoline that you pump in your car will likely contain natural impurities, deposits, and contaminants that settle in the fuel tank and could potentially cause damage to parts like the fuel injectors. As you might guess, a fuel filter simply acts as a barrier, keeping potentially damaging elements from playing havoc on the rest of your vehicle. Since it does undergo a lot of heavy use during the regular lifespan of your vehicle, it slowly gathers and holds those contaminants, and eventually, if not attended to, will begin to restrict flow and eventually plug up.  

How often to replace a fuel filter can depend on a number of things. Fuel filters on older cars will often last one and a half to two years, but some can last longer. Some newer cars have “lifetime” filters that may be built into the fuel pump and do not need to be replace on a service interval. Check your owner’s manual to determine exactly how long the usefulness of your fuel filter lasts. If you end up with a tank of dirty fuel or start to notice symptoms that indicate the fuel you’re using is no longer being filtered properly, you may have to switch it out sooner than expected.

How Long Does a Fuel Filter Last? 

Some but not all cars have a fuel filter element that can be replaced. On gas-powered cars, it’s usually underneath, clipped or bolted to the frame rail. On diesel vehicles, it’s usually in the engine compartment and has the same style as an oil filter. For most cases, the fuel filter needs to be replaced every 20,000 to 30,000 miles, while diesel vehicles often are slightly shorter intervals. The best way to tell your vehicle’s interval is to check the maintenance guide provided along with your owner’s manual.  

Some vehicles don’t have a replaceable fuel filter. Rather, they have a screen on the fuel pump that filters out particles in the tank, and these filters aren’t serviced unless you’re working on the fuel pump itself. 

Signs of a Bad Fuel Filter 

As fuel flows through the filter, pleated material strains out any contaminants on the way to the engine. It could be dirt, salt, or any moisture or debris that gets kicked into the massive tank when the gas station gets a delivery. When the fuel filter gets full of this material, it restricts fuel flow to the engine. Symptoms are sure to result eventually. 

  • Power loss when under load
  • Check engine lights is on
  • Engine runs rough or stalls
  • Your engine won’t start
  • Fuel pump quits
  • Decreased fuel economy

Power Loss when Under Load

Restricted fuel supply to the engine might allow for proper fuel pressure while the engine is idling. However, when you’re accelerating or pulling a load, the demand for fuel is much greater. A blocked fuel filter prevents the fuel rail from staying full of fuel, restricting the amount of power your engine can produce. 

Check Engine Light is On 

If the injectors don’t receive enough pressurized fuel, there may not be enough sprayed into the cylinders to be burned. A ‘P0171 System Too Lean’ code could be stored in the powertrain control module, triggering the Check Engine Light. 

Engine Runs Rough or Stalls

Without sufficient fuel supply, the engine can stumble or stall while driving or while idling. Think of it like pinching the straw while you try to drink your soda through it. When you close off the straw, you’re unable to keep the flow of energy-producing fluid going. 

Your Engine Won’t Start

When you turn the key, the fuel pump pressurizes fuel going into the supply line. A clogged fuel filter may prevent fuel from pressurizing the same in the section between the filter and the engine. Your engine may not fire up since it’s starved of fuel, or it might fire up for a second and die again. 

Fuel Pump Quits

Excessive demand for fuel can create strain on the fuel pump. It’s constantly cycling at peak performance, trying to force fuel into a restricted supply line. It can cause the fuel pump relay to kick off, the fuse to burn, or the fuel pump to quit altogether. 

Decreased Fuel Economy

It might seem counterintuitive, but a blocked fuel filter can actually cause higher fuel consumption. The PCM believes that the air-fuel mixture is lean and, to compensate, commands more fuel to mix with the air being sucked into the engine to get the amount of power you’re commanding from your car. Though it’s not performing as well, you’re burning more fuel than if the fuel was moving at the right volume. 

How Do You Replace a Fuel Filter?

If you see signs you need to change your fuel filter, then it’s probably time to start thinking about whether you can replace it yourself or if you need some professional help. While the exact process for changing the filter can vary a lot depending on your vehicle, it is possible to switch it out yourself. 

Remember, that you are going to be dealing with gasoline, and leaking gasoline once you crack open the fuel line, so exercise extreme caution! Be sure to read your repair manual or consult online how to properly relieve the fuel system of pressure before cracking open the fuel line, or what steps need to be taken to open the fuel system. 

The most common location for a fuel filter is in one of the fuel lines coming from the fuel tank, mounted near the tank on the vehicle’s frame. Several are also located inside the engine compartment, while others are non-serviceable and located within the fuel pump assembly, in the fuel tank. 

Most fuel systems on cars built in the last 20 years have quick-connect clips or unions that hold the lines together, and hold the fuel filter in-line for a leak-free seal. With the right tools, such as OEM 25150 or 24681, you can disconnect these fittings. Keep in mind, they can often be tricky to disconnect. If you do not have a lot of experience with fuel system maintenance, it may be best to get help from a professional mechanic, which you can search your area for one of our Preferred Shops here.  

Keep in mind, a fuel filter is made to be a service-interval part, rather than a failure part. Follow your vehicle’s OEM guidelines (check the owner’s manual) on when to change a fuel filter, or, if you’ve purchased a vehicle with over 100,000 miles and no indication the fuel filter has been changed, it’s a great idea to change it. The good news is that fuel filters can be a relatively affordable part, especially if you buy the parts and do the work yourself. A new filter can cost as little as around fifteen dollars in some cases, and even if you go to a pro, the costs of a replacement generally stays around $200.

How to Check a Fuel Filter

Once you remove a fuel filter, you can tell whether it’s the source of your problem by a simple blow-test. 

First, attempt to drain all the gas out of the fuel filter the best you can. Find the inlet to the fuel filter (should be labeled as either “in” or have an arrow pointing to the direction of the fuel flow) and clean that inlet with a shop towel.

Now, place a disposable rag or shop towel on your workbench, and gently blow into the inlet of the fuel filter, aiming down towards your shop rag on the bench. You should be able to easily blow into the filter without much resistance. With a plugged fuel filter, you won’t be able to. With a heavily restricted or clogged fuel filter, it will be hard.

Remember, gasoline is gross, doesn’t taste good, and is flammable, so be sure to exercise extreme caution. Leave any rags or towels long enough to dry outside before disposing them, and NEVER throw any old fuel or rags wet with gasoline into the trash.

Keeping Up with Fuel Filter Maintenance

Fuel filter problems generally won’t happen with proper maintenance. If you start noticing problems with your engine running strangely and experience loss of power and poor gas mileage, the fuel filter is a likely suspect on the fuel side, and an easy one to check off and change. 

Luckily, a new fuel filter should not cause too much of a dent in your bank account and even if you find that it doesn’t solve the issue, you are still replacing a maintenance item that needs to be replaced soon enough. Following the recommended change intervals in your owner’s manual is key to maintain optimal vehicle health, and in this case, the health of your fuel system. Waiting until you are starting to experience issues with your fuel filter may cause bigger fuel delivery issues to deal with beyond a clogged filter. 

For any advice on recommended maintenance, like fuel filters, come see us at any AutoZone location.  

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