Fuel Systems

Fuel Systems

PT- 264

By: Bobbie Day

3/28/2005

In this report I will explain the fuel systems in an automobile. I will cover different parts and how they work. First thing to do is explain how the fuel system works. The purpose of the fuel system is to store and supply fuel to the cylinder chamber where it can be mixed with air then vaporized and burned to produce energy. The fuel, which can be either gas or diesel is stored in a fuel tank. A fuel pump draws the fuel from the gas tank through lines and brings it through a fuel filter. Next it goes to either a carburetor or fuel injector and then delivered to the cylinder chamber for combustion.

We will start with the fuel tank. A fuel tank comes in many different sizes depending on how much space is available. Most cars and trucks have only one tank but some trucks have two. Fuel tanks can be made of 3 different things. These are pressed corrosion-resistant steel, aluminum, or molded reinforced polyethylene plastic. The fuel tank has internal baffles or surge plates to prevent the fuel from sloshing back and forth. If you hear splashing in the tank on acceleration or deceleration, this means that the baffles could be broken. All tanks have a fuel filler pipe, a fuel outlet line to the engine and a vent system. All catalytic converter cars are equipped with a filler pipe restrictor so that led

fuel, which is dispensed from a thicker nozzle, cannot be introduced into the fuel system. All modern fuel tanks include devices that prevent vapors from leaving the tank. All fuel tank designs provide some control of fuel height when the tank is filled. This is achieved by using vent lings within the filler tube or tank. With this design only 90% of the tank is ever full, leaving 10% for expansion. Some vehicles have a over filling limiting valve to prevent overfilling of the tank.

Fuel is drawn from the tank by an in-tank or chassis-mounted fuel pump. The fuel pump is the device that draws the fuel from the fuel tank through the fuel lines, to the fuel filter and then to the engine’s carburetor or injectors. There are two types of fuel pumps: mechanical and electrical. The mechanical fuel pump is bolted on the side of the engine block or on the side of the cover of the timing gear. The electrical fuel pump is located inside or outside of the fuel tank.

The diagram below is of an electrical fuel pump.

Electric fuel pumps offer important advantages over mechanical pumps. Because electrical pumps maintain constant fuel pressure, they aid in starting and reduce vapor lock problems. There are four basic types of electric fuel pumps and they are: diaphragm, plunger, bellows, and impeller or rotary. In-tank electric fuel pumps are usually rotary type. The diaphragm, plunger, and bellows are usually called the demand style. This means, when the ignition is turned on that the pump begins operation. All types shut off automatically when the fuel line is pressurized. So when there is a demand for more fuel, then the pump gives more, and less for when less is needed.

In the diagram below is a mechanical fuel pump.

Next are the fuel lines. Steel lines and flexible hoses carry the fuel from the tank to the engine. When servicing or replacing the steel lines, copper or aluminum must never be used. Steel lines must be replaced with steel. When replacing flexible