308 Auto Engine Repair Copyright by Goodheart-Willcox Co., Inc. Electrical connector Fuel supply line Tank mounting flange In-tank pump Pump inlet filter Fuel Float Variable resistor assembly Supply line check valve Return line check valve Fuel return line Figure 15-3. This is an in-tank electric fuel pump. Note the fuel strainer, pump motor, fuel return, and float. (Chrysler) Warning: The fuel line may contain fuel under pressure as high as 50 psi (345 kPa) even when the ignition key is off. Always relieve fuel pressure before disconnecting any EFI fuel line. Loosen lines carefully until you verify the system is not under pressure. Most EFI systems have a special relief valve (test or service fitting). Or, the pressure regulator may allow pressure relief for bleeding pressure back to the fuel tank. Fuel Filters Fuel filters stop contaminants such as rust, water, corrosion, and dirt from entering the fuel metering system. A fuel filter, or strainer, is normally located on the fuel tank pickup tube. This is a coarse filter that blocks larger debris. A second fuel filter may be located in the main fuel line or inside the fuel pump to block smaller debris. Fuel Filter Service Fuel filter service involves periodic replacement or cleaning of system filters. It may also include locating clogged fuel filters. A clogged fuel filter can restrict the flow of fuel to the fuel metering system. Fuel filters can be located: • In the fuel line before the fuel injectors. • In the fuel line right after the fuel pump. • Inside the fuel pump. • Inside the injector body (strainer type). • A fuel strainer is also located in the fuel tank on the end of the fuel pickup tube. When in doubt, refer to the service manual for filter loca- tions, service intervals, and related information. Fuel Pump A fuel pump produces fuel pressure and flow. Electric fuel pumps are commonly used on late-model vehicles. A small electric motor spins an impeller, which forces fuel through the system. The fuel pump operation is controlled by an on-board computer. An electric fuel pump can be located inside the fuel tank as part of the fuel pickup unit, Figure 15-3. It can also be located in the fuel line between the tank and engine. Many in-tank fuel pumps also incorporate a sending unit for operating the fuel gauge in the dash. In addition to an electric fuel pump, direct injection systems are equipped with a high-pressure mechanical fuel pump that is mounted on the engine and powered by an eccentric on the engine’s camshaft, Figure 15-4. The electric fuel pump feeds fuel to the mechanical fuel pump. The mechanical pump supplies fuel under high pressure to the fuel rail and the injectors. Pressures produced by the mechanical fuel pumps can range from 1500–2000 psi (10–14 MPa). Note: The mechanical fuel pumps used in carbureted fuel systems produce a relatively low pressure (4–6 psi [30–40 kPa]). These pumps bolt to the side of the engine block and are driven by a lobe on the camshaft. Fuel Pump Service Fuel pumps can fail after prolonged operation. Fuel pump problems usually show up as low fuel pressure, inad- equate fuel flow, abnormal pump noise, or fuel leakage from the pump. Low fuel pump pressure can be caused by worn motor brushes, worn motor bushings, clogged strainer, poor elec- trical connections, and similar troubles. Fuel pump leaks are caused by physical damage to the pump body or deterio- ration of the diaphragm or gaskets. Most electric fuel pumps make a slight buzzing or humming sound when running. Only when the pump noise is abnormally loud should an electric fuel pump be con- sidered faulty. A clogged tank strainer is a common cause of excess electric fuel pump noise. If an electric fuel pump is starving for fuel the pump will buzz loudly because it is pumping air and not fuel. Pump speed can increase because fuel is not entering the pump properly. Electric fuel pumps can also make noise after prolonged service when the motor bushing becomes worn. If the pump is not pumping, check supply voltage to the pump. If there is voltage at the pump, check for a clogged fuel filter. If these are not the problems, the pump may need to be replaced. Replacing a fuel pump is a relatively simple task, Figure 15-4. Refer to the service manual for specific instruc- tions on pump replacement. Remember to: • Relieve system fuel pressure. • Place a rag around the pump fittings when loosening.