Car Fuel System

Table Of Contents

The Fuel System

The fuel system is the system that pumps fuel into the cylinders of the internal combustion engine and mixes it with the perfect amount of air for combustion. There are two types of fuel systems: fuel injection and carburetors.

lllustration of a carburetor.

Prior to 1985 most vehicles used a carburetor. A carburetor uses a venturi (narrowed passage within the carburetor) to draw fuel from a float bowl based strictly on the volume of air flowing through the carburetor. A carburetor is a primitive method of mixing air and fuel. it is far less efficient than modern fuel injection. That’s why all modern cars today are built with fuel injection.

How a Fuel Injection System Works:

Fuel injection is a complex electrical circuit using multiple sensors as inputs to a PCM (powertrain control module, also called the computer). The PCM then interprets the inputs from these sensors and produces a PWM (pulse width modulated) signal. A PWM signal is digital on/off signal. This translates into how much fuel is injected into the engine.

The PCM then receives feedback signals from oxygen sensors. An oxygen sensor is a sensor that checks the air-fuel ratio by monitoring exhaust gas at or near the exhaust

manifolds. Using this information, the PCM can adjust fuel trim accordingly to keep the engine running clean, long, and efficiently. This is one of the main reasons newer automobiles last so much longer, burn less fuel, and have cleaner emissions.

illustration of a fuel injector.

Fuel Filter and Air Filter:

There are two filters that protect the fuel system and engine: the fuel filter and the air filter. The fuel system is very sensitive to contamination and debris. A small amount of contamination can cause severe problems in any fuel system. Therefore, these filters are critical for protecting the fuel system and engine.

A fuel filter (white) next to the air filter compartment (circular black part)

When you fill your vehicle with fuel from a gas station, the fuel will have contaminants. Between the fuel tank and the engine, the fuel passes through a sock filter which prevents large contaminants from passing through. Then the fuel will pass through the fuel filter which prevents small contaminants from passing. Anything that passes through the fuel filter can pass through the rest of the fuel system. Refer to the owner’s manual to find the manufacturer's recommendation for the mileage at which the fuel filter should be changed.

An air filter protects the engine from dust and dirt entering the combustion chamber through the air intake system. Any dirt in the engine can cause engine wear and eventually lead to engine failure. Therefore, an air filter, like the fuel filter, is also a critical component in any internal combustion engine. The air filter is inspected with every oil change and it is changed as needed.

Various air filters.

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