The fuel filter is the fuel system’s first line of defense against contaminants. The filter traps any dirt or rust particles that have been sucked up by the fuel pump inside the fuel tank so they can’t reach the fuel injectors. The injectors have a small screen in their fuel inlet connection to prevent large particles from entering, but the screen provides virtually no protection against microscopic particles that can wear and damage the tight-fitting valve inside the injector. That’s why the fuel filter is so important.
The fuel filter may be located somewhere in the fuel line (engine compartment, under the vehicle or near the fuel tank), or it may be part of the fuel pump module assembly inside the fuel tank if the vehicle has a “returnless” EFI system. Most of these in-tank filters are “lifetime” filters with no recommended service interval. The filter usually only needs to be replaced if the fuel pump has failed or the fuel tank is contaminated with dirt or rust.
Fuel filters on most fuel-injected engines (except those with returnless EFI systems) flow a lot more fuel than the engine actually burns. That’s because the fuel continually recirculates from the engine back to the tank when the engine is running. So the same fuel is actually filtered over and over again every time it makes the loop from the tank to the engine and back.
Most fuel filters will trap particles 3 microns or larger in size, and some will trap particles that are even smaller. And just like air and oil filters, filtering efficiency goes up the dirtier the filter gets. But at the same time, so does the resistance to flow.
Though the trend has been to move to longer and longer service intervals, many technicians still recommend replacing in-line fuel filters every 30,000 to 50,000 miles for preventive maintenance.
A plugged fuel filter will restrict fuel flow to the engine. The drop in pressure may not be noticeable at idle, but as engine speed goes up, there may be a significant drop in pressure and a decrease in flow.
Symptoms of a restricted fuel filter include a loss of high-speed power, lean misfire, hesitation and even hard starting.
A new fuel filter should always be installed when a fuel pump or fuel injectors are being replaced. If a new filter becomes clogged shortly after it has been installed, the inside of the fuel tank is probably dirty or rusty. The fuel tank needs to be inspected and cleaned as needed or replaced if it is a steel tank and is badly corroded inside. Aging plastic fuel tanks can even deteriorate inside and shed particles that may clog a fuel filter.
Note: Inexperienced DIY customers can easily damage a fuel line if they do not have the proper tools for changing an in-line fuel filter that is mounted with a quick-release connection. A special disconnect tool is required to remove the fuel lines from the filter. Prying or forcing the connection apart will usually destroy the fuel line.
If rubber hoses connect to the fuel filter, they should be inspected and replaced if cracked, damaged or leaking. Fuel hoses more than 10 years old should be replaced with new EFI-rated hoses.