Why Is My Fuel Filter Clogged?

A clogged fuel system can cause drivability problems. Replacing the fuel filter is a quick fix, but finding why the filter is clogged is important.

A dirty or clogged fuel filter can starve an engine of fuel and is always a likely cause of low engine power. Most modern vehicles with fuel injection systems use filters rated to trap debris between 10 and 30 microns (a micron is .001mm in diameter) a human hair is approximately 70 microns (.08mm). Due to their abrasive nature, even microscopic dirt or grit that gets past a faulty or dirty fuel filter can damage your engine.

What Is a Fuel Filter?

Fuel filters come in many shapes and sizes and are designed to do one thing: keep dirt, rust, scale and other impurities from entering and damaging the fuel pump, fuel injectors and engine without effecting fuel pressure. Most vehicles have two fuel filters, one in the fuel tank (called a strainer) and one located in the main fuel line. Filtering material is made from plastic or specially coated paper that traps foreign particles that can interrupt the fuel supply.

What Are the Signs of a Clogged Fuel Filter?

Poor Engine Performance

Under heavy or high-speed acceleration, a clogged fuel filter may cause the engine to randomly hesitate, surge or sputter. Although there may be no symptoms under normal driving conditions, a clogged fuel filter will starve the engine of the extra fuel needed during hard acceleration.

Hard Starting

Unless completely blocked, rarely will a bad fuel filter keep your engine from starting. However, a dirty fuel filter can decrease fuel pressure causing longer than usual cranking before the engine starts.

Stalling

Repeated stalling while driving, especially at low-speeds or coming to a stop could signal a dirty fuel filter. Depending on the severity of the clog, your car may start right back up without any noticeable loss of power. As the clog worsens, and fuel delivery becomes more sporadic, stalling becomes excessive.

Random Misfire or Rough Idle

Low fuel pressure from a partially blocked filter results in a lean fuel condition and engine misfire. This can cause poor fuel mileage, rough idling and possibly engine backfire or increased engine smog.

Fuel System Part Failures

A clogged fuel filter prevents the correct amount of fuel from reaching the engine. Trying to compensate for low fuel pressure, fuel pump pressure increases causing the pump to overheat, become noisy and fail prematurely. A saturated fuel filter that lets dirt and grit bypass the filter can clog fuel injectors, causing them to not fully open or close. This can cause any number of rich or lean fuel mixture drivability issues.

Check Engine Light (CEL)

Drivability troubles caused by a clogged fuel filter can cause emission or fuel pressure sensors to illuminate the CEL, alerting the driver of a problem. In addition to turning on the CEL, the computer stores a “trouble code” in its memory. Many big box auto parts stores will read the codes for free to help identify the source of the problem.

What Causes a Clogged Fuel Filter?

  • Rust from a decaying steel fuel tank, steel fuel lines and fittings
  • Sediment from poor quality fuel
  • Silt deposits or water from your filling stations’ in-ground storage tanks
  • Dirty air filter
  • Moisture (from condensation) build-up in the fuel tank
  • Dust and dirt entering the tank while filling the fuel system
  • Failing fuel pump
  • Off-roading

How To Fix a Clogged Fuel Filter

Replacing — never cleaning — is the only “fix” for a clogged filter. However, if you are constantly replacing a clogged fuel filter, there’s probably a build-up of muck in the fuel tank. Your entire fuel system will most likely need to be disassembled, cleaned and flushed — including removing or replacing the fuel tank. A job for the pros, this is a time–consuming and extremely expensive repair.

What Does It Cost to Fix a Clogged Fuel Filter?

Depending on your make, model, year and engine, a main line fuel filter usually costs around $20. You can replace the main line fuel filter yourself. If you go the DIY route, check your owner’s manual for filter location (the correct part number may also be listed). Set aside at least an hour. Again, depending on your vehicle’s specifics, it should take your mechanic less than a half-hour, and cost between $65 and $125 for them to replace a fuel filter. Let your mechanic replace the in-tank fuel tank strainer. Expect to pay between $250 and $500 for this service.

SAFETY FIRST!

If you are going to replace a fuel filter yourself, be sure the engine is cool, you have the proper tools and you release fuel system pressure by pulling the fuel pump fuse (check the owner’s manual for its location) and then running the engine until it shuts off. Releasing fuel pressure is critical because you do not want gas spraying all over the engine or ground — be safe and have a fire extinguisher nearby anyway — and replace all O-rings, gaskets and seals and check that all mounting brackets and retaining clips are correctly reinstalled. Start your car and check for leaks after installing the new fuel filter.

The Last Word

To reduce drivability problems, maintain optimum performance, reduce tailpipe (smog) emissions and extend the life of your vehicle, replace the fuel, air, oil and transmission filters (and fluids) according to your vehicle manufacturer’s recommended service schedule, or sooner under harsh, dusty or dirty driving conditions.

Bob Lacivita
Bob Lacivita is an award-winning ASE and General Motors auto technician, educator and freelance writer who has written about DYI car repairs and vehicle maintenance topics. His work has been featured in The Family Handyman, a Reader's Digest book and Classic Bike Rider magazine. He has been a career and technical educator for 25 years teaching automotive technology, as well as writing state, federal and organizational foundation grants. He also helped design a unique curriculum delivery model that integrates rigorous, relevant academic standards seamlessly into career and technical education.