Signs & Symptoms of a Blocked Air Filter on a Car

by Alexander Eliot
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In an automotive engine, the air filter acts as a barrier between the intake system and the ambient air required for fuel combustion. A congested or blocked filter requires the engine to work much harder to draw in air, leading to numerous performance issues. The signs and symptoms of a blocked air filter make the problem relatively easy to diagnose. Furthermore, you can quickly inspect and replace the air filter by following the service procedure recommended in your car owner's manual.

Diminished Power and Acceleration

To generate power, the engine requires an adequate amount of air to mix with fuel for combustion. A blocked air filter restricts the airflow into the engine, thus reducing the power output. This is especially evident under heavy acceleration, as the engine requires an increasing amount of airflow to feed the cylinders as its rpm rises. With a blocked air filter, the engine may feel hesitant under acceleration, especially in the upper rpm range. In extreme cases, the engine may be unable to accelerate beyond a certain speed or rpm due to inadequate airflow.

Sputtering and Stalling

A severely clogged air filter can cause the engine to sputter or even stall. When the engine is unable to draw in an adequate amount of air, it can experience an overly rich air-to-fuel ratio. This leads to an inefficient combustion process, with excess fuel remaining in the cylinders after each piston cycle. With an extremely rich air-to-fuel ratio, the engine may hesitate and sputter when accelerating and may even stall when you lift off the throttle. In less extreme cases, the abundance of leftover fuel in the cylinders will create a strong gasoline smell from your car's exhaust system when the engine is running.

Fuel Economy

Older vehicles with carbureted engines will have a significant drop in fuel economy when the air filter is blocked. Since a blocked filter restricts the airflow into the intake, the engine is not able to achieve a proper air-to-fuel ratio, and thus the efficiency of the internal combustion process is severely reduced. However, most modern vehicles with fuel-injected engines will have a much less dramatic drop in fuel economy. In addition to air-to-fuel ratio issues, a clogged filter slightly reduces fuel economy by requiring the engine to work harder to draw air through the filter.

Inspection and Replacement

Refer to your vehicle owner's manual to find out the suggested maintenance schedule and replacement procedure for the air filter. Regardless of the mileage interval suggested in the owner's manual, you should inspect the intake system immediately if your vehicle displays the symptoms of a blocked filter. On most cars, the air filter is inside a black plastic air chamber, accessible in the engine bay. Remove any metal clips and/or screws securing the plastic lid, then lift it free to access the filter. If the filter is clogged with dirt and debris, replace it with a new unit before reinstalling the air chamber lid.

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