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Symptoms of a Bad Fuel Filter

By Stephen Fogel, March 14, 2018

As the name suggests, your fuel filter’s primary function is to remove any impurities from your car’s fuel supply. If your fuel filter hasn’t been serviced for a while, it will become filled with dirt and other bad things that can potentially end up in the fuel injectors and engine. If left unchecked, you could end up with much more serious problems. 

What is a fuel filter?

The fuel filter is placed somewhere between the fuel tank and the engine. Some fuel filters are placed inside the fuel tank, while others may be underneath the vehicle, or under the hood. 

Gasoline is an extremely clean substance — until it leaves the refinery. From that point, it has many opportunities to take on contaminants as it’s transported, stored and then pumped into your tank. As the gas flows from your tank to the engine, the fuel filter removes dirt and other abrasive particles that can clog your fuel injectors and cause damage to the finely machined surfaces of your engine. 

A fuel filter uses a simple design, similar to an oil filter or an air filter. A pleated material filters the fuel as it is through the filter housing. Any debris becomes trapped in the filter material, and clean fuel leaves the filter on its way to the fuel injectors.

The long-term health of your vehicle depends on a clean fuel filter. If you notice any of these symptoms of a failing one, have a mechanic inspect your car to see if the fuel filter needs changing.

Get it diagnosed by a professional
 

Symptoms of a fuel filter problem

Hard starting: Difficulty getting your engine started can be one of the first signs of a fuel filter that’s beginning to clog. Because the fuel flow is restricted and inconsistent, it may take a lot of cranking to fire up the engine. While there may be other causes for this problem, the fuel filter is an easy place to start the diagnosis. 

Engine hesitation: A malfunctioning fuel filter can cause the engine to hesitate under a variety of conditions, including starting from a stop, accelerating and driving up an incline. The obstructed flow of fuel through the filter is insufficient for the car’s needs, so you would feel this hesitation or stumbling, which can also feel like a “bucking” sensation. This can be dangerous — a hesitating car can be bad news when you have to make a quick decision about merging or getting through an intersection.

Misfires and a decrease in power and performance: Without sufficient fuel, your engine can misfire and produce much less power than it should. This problem may come and go as you drive, as the partially clogged filter allows varying amounts of fuel to pass through it. You may also notice a jerking or stuttering coming from your engine.

Check engine light comes on: While the fuel filter is not directly connected to the engine computer, a blocked fuel filter can trigger a variety of trouble codes, including:

  • Low fuel pressure
  • Lean running condition
  • Oxygen sensor fault
  • Mass air flow sensor fault
  • Engine misfiring

If your check engine light has come on, proper diagnosis is essential. The actual cause of the problem may be a side effect of a bad fuel filter. The filter should be checked before you start replacing expensive parts of your emissions control system.

Stalling: You are able to start your engine, but when you start driving, it stalls out. You can restart it, but once you start moving, it stalls again. This could mean that your fuel filter is allowing just enough fuel through it to get your engine started, but not enough for the demands of acceleration and cruising. The fuel supply flowing through a dirty filter may also be intermittent, cutting off periodically and starving your engine of the fuel it needs.

Engine won’t start: A completely clogged fuel filter will allow no fuel through. No fuel means no start. You crank and crank the starter, but the engine won’t catch. Your vehicle won’t run again until the faulty fuel filter is dealt with.

Power varies at different speeds: Sometimes, a vehicle with a dirty fuel filter can operate just fine at higher speeds, but have driveability problems at lower speeds. In these situations, the higher fuel pressures produced during high-speed operation can mask a problem. High fuel pressures can overcome an obstructed filter, but as soon as you slow down, the smooth operation goes away, replaced by some of the symptoms listed here. The lower fuel pressures at lower speeds cannot push enough fuel through the dirty filter.

Rough engine idle: A bad fuel filter can cause rough idling. You may hear the engine stutter or vibrate as it gets starved of fuel. Your tachometer may also show this with a needle that moves up and down erratically at the low end of the range. 

Fixing your fuel filter problem

Because of the fire risk of working with the fuel system, it’s best to leave this job to a professional mechanic. 

A fuel flow test can be used to check for restrictions inside the fuel filter. The fuel pump can also be checked to determine whether it is under excess load from a blocked filter. 

The actual fix is straightforward: the old fuel filter is replaced with a new one. Expert technicians will often cut open the old fuel filter. This allows a more complete diagnosis, and can provide many clues to other problems that may exist in your fuel system. The type of contaminants found, including rust particles and water, can all point to other issues affecting the fuel tank, pump and injectors.

If you are experienced and have the confidence to do the job yourself, know that most cars made in the past 30 years or so use quick-release fittings to contain the high pressure used in fuel systems. It’s important to use the correct tools for the specific type of fittings in your fuel system.

 

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