306 Auto Engine Repair Copyright by Goodheart-Willcox Co., Inc. Fuel tank pressure sensor Fuel pressure regulator Fuel rail Fuel vapor pipe Fuel return pipe Fuel gauge sending unit Fuel tank evap valve Fuel pump Fuel fill cap Fuel tube/quick-connect fittings Fuel tank Fuel feed pipe Fuel filter Fuel injectors Figure 15-1. Note the location of typical fuel supply system components. (Honda) As an engine technician, you must have a basic knowl- edge of the fuel and emission control systems. You must be able to quickly determine if problems are in either of these systems or the engine itself. This chapter covers the prin- ciples behind the fuel and emission control system. Basic troubleshooting of these systems is also covered. Fuel System Proper engine operation depends on an adequate sup- ply of clean air and fuel. Without the correct mixture of fuel and air, an engine will perform poorly. This section of the chapter summarizes the most important information on air filters, fuel filters, and fuel pumps. It provides the informa- tion most commonly used by an engine technician. A fuel system can be divided into three subsystems: • Fuel supply system. • Air supply system. • Fuel metering system. It is important that you understand the components included in each system when trying to diagnose and repair engine problems. Fuel Supply System The fuel supply system provides filtered fuel under pressure to the fuel metering system. It must also provide for storage of the fuel. See Figure 15-1. Fuel Tanks An automotive fuel tank must safely hold an adequate supply of fuel for prolonged engine operation. The size of a fuel tank partially determines a vehicle’s driving range. Fuel tank capacity is the rating of how much fuel a tank can hold when full. An average fuel tank capacity is about 12 to 25 gallons (45 to 95 liters). A fuel tank pickup unit extends down into the tank to draw out fuel. A coarse filter is usually placed on the end of the pickup tube to strain out larger debris. Sometimes, the pickup unit also operates the fuel gauge. The fuel tank filler neck is the extension for filling the tank with fuel. The filler cap fits on the filler neck. Fuel Lines and Hoses Fuel lines and fuel hoses carry fuel from the tank to the engine. A main fuel line connects the tank to the engine. Fuel is pulled or pushed through this line to the engine, Figure 15-2. Fuel lines are made from plastic, nylon, or double-wall steel tubing. Plastic and nylon tubing may be used in some areas of the fuel system to reduce the possibility of rust and corrosion. A fuel line must be strong enough to withstand the constant and severe vibrations produced by engine and vehicle operation. Fuel hoses can be made of nylon or synthetic rubber covered with a plastic insulator. Hoses are used when move- ment between two or more parts can occur, such as between the body and the engine. A fuel return system helps cool the fuel and prevent vapor lock. Vapor lock occurs when bubbles form in the overheated fuel and disrupt normal fuel flow. A second return fuel line is used to carry excess fuel back to the tank. This keeps cool fuel constantly circulating through the system. Warning: Always keep a fire extinguisher handy when working on a fuel system. During a fire, a few seconds can mean the difference between life and death.