Although air and fuel filter maintenance is usually considered a "no-brainer" by most import repair shops, advancing technology is changing the way we should be performing air and fuel filter maintenance.
To illustrate, recommended replacement intervals for air filters are now ranging between 15,000 and 75,000 miles. Fuel filter replacement intervals vary from between 20,000 miles to 150,000 miles, to “lifetime” in some applications. Modern fuel quality is so good that many import manufacturers leave the replacement interval to the technicians’ discretion. In any case, it’s important to compare perception with reality in the modern air and fuel filter markets. See Photo 1 .
Photo 1: The positive short-term fuel trims on this data screen can indicate that the fuel filter is clogged or the fuel pump is defective.
PERCEPTION AND REALITY
Despite the advanced engineering invested in modern intake air systems, many veteran and amateur technicians continue to believe that an air filter is a necessary restrictive device used to prevent air-borne dirt from entering an engine. Many also believe that removing an air filter or installing a larger capacity air filter will improve high-speed engine performance and fuel economy.
The reality is that modern air filters , even when liberally coated with dirt and air-borne debris, have more than enough surface area to support air flow during normal driving conditions. Even if air flow through the air filter becomes slightly restricted, the powertrain control module (PCM) will use the mass air flow (MAF) sensor input to match the volume of incoming fuel with the volume of incoming air. So, even while horsepower might be slightly reduced due to restricted air flow, fuel economy and power won’t suffer during normal driving conditions.
Many owners and technicians routinely remove, inspect and, perhaps, replace air filters during each oil change interval. Although a few import manufacturers recommend inspecting an air filter during an oil change, most recommend inspecting and replacing it at specified intervals. In many cases, frequent inspections allow dirt to fall into the filter housing and the housing is often damaged through repeated disassembly. In most cases, following manufacturers’ inspection and replacement intervals saves a lot of wear and tear on the air filter housing and on the customer’s wallet!
AIR FILTRATION SYSTEMS
Notice that I attached the word “systems” onto the words “air filtration.” To illustrate, the modern air filtration system must not only separate air-borne dirt from the inlet air, it must also dampen undesirable intake air noise and, most important, remove turbulence from the incoming air. To achieve these goals, modern air filtration systems combine a small cross-sectional area in the air inlet with a larger cross-sectional area i...
