Fuel System

The fuel system is made up of the fuel tank, pump, filter, and injectors or carburetor, and is responsible for delivering fuel to the engine as needed. Each component must perform flawlessly to achieve expected vehicle performance and reliability.

FUEL TANK

Tank location and design are always a compromise with available space. Most automobileshave a single tank located in the rear of the vehicle. Fuel tanks today have internalbaffles to prevent the fuel from sloshing back and forth. If you hear noises from the rearon acceleration and deceleration the baffles could be broken. All tanks have a fuel fillerpipe, a fuel outlet line to the engine and a vent system. All catalytic converter cars areequipped with a filler pipe restrictor so that leaded fuel, which is dispensed from athicker nozzle, cannot be introduced into the fuel system. All fuel tanks must be vented.Before 1970, fuel tanks were vented to the atmosphere, emitting hydrocarbon emissions.Since 1970 all tanks are vented through a charcoal canister, into the engine to be burnedbefore being released to the atmosphere. This is called evaporative emission control andwill be discussed further in the emission control section. Federal law requires that all1976 and newer cars have vehicle rollover protection devices to prevent fuel spills.

FUEL LINES

Steel lines and flexible hoses carry the fuel from the tank to the engine. Whenservicing or replacing the steel lines, copper or aluminum must never be used. Steel linesmust be replaced with steel. When replacing flexible rubber hoses, proper hose must beused. Ordinary rubber such as used in vacuum or water hose will soften and deteriorate. Becareful to route all hoses away from the exhaust system.

FUEL PUMPS

Two types of fuel pumps are used in automobiles; mechanical and electric. All fuelinjected cars today use electric fuel pumps, while most carbureted cars use mechanicalfuel pumps. Mechanical fuel pumps are diaphragm pumps, mounted on the engine and operatedby an eccentric cam usually on the camshaft. A rocker arm attached to the eccentric movesup and down flexing the diaphragm and pumping the fuel to the engine. Because electricpumps do not depend on an eccentric for operation, they can be located anywhere on thevehicle. In fact they work best when located near the fuel tank.
Many cars today, locate the fuel pump inside the fuel tank. While mechanical pumpsoperate on pressures of 4-6 psi (pounds per square inch), electric pumps can operate onpressures of 30-40 psi. Current is supplied to the pump immediately when the key isturned. This allows for constant pressure on the system for immediate starting. Electricfuel pumps can be either low pressure or high pressure. These pumps look identical, so becareful when replacing a fuel pump that the proper one is used. Fuel pumps are rated bypressure and volume. When checking fuel pump operation, both specifications must bechecked and met.

FUEL FILTERS

The fuel filter is the key to a properly functioning fuel delivery system. This is moretrue with fuel injection than with carbureted cars. Fuel injectors are more susceptible todamage from dirt because of their close tolerances, but also fuel injected cars useelectric fuel pumps. When the filter clogs, the electric fuel pump works so hard to pushpast the filter, that it burns itself up. Most cars use two filters. One inside the gastank and one in a line to the fuel injectors or carburetor. Unless some severe and unusualcondition occurs to cause a large amount of dirt to enter the gas tank, it is onlynecessary to replace the filter in the line.