Fuel Supply System Chapter 21 Lesson 1

Fuel Supply System Draws fuel from the fuel tank and forces it into the fuel metering device Fuel metering devices fed by the fuel supply system include: gasoline injection system diesel injection system carburetor

Fuel Supply System Components The basic parts of a fuel supply system include: Fuel tank stores gasoline, diesel fuel, or alternate fuel Fuel lines carry fuel between the tank and the fuel metering system

Fuel Supply System Components Fuel pump draws fuel from the tank and pumps it to the fuel metering system Fuel filters remove contaminants in the fuel

Fuel Tank Must safely hold an adequate supply of fuel for prolonged engine operation Normally mounted in the rear of the vehicle under the trunk or back seat in a passenger car Fuel tank capacity varies from about 12 to 25 U.S. gallons (45-95 liters)

Fuel Tank Construction Fuel tanks are made of either thin sheet metal or plastic Metal tanks are made by soldering or welding two formed pieces of sheet metal together a zinc alloy is plated to the sheet metal to keep the tank from rusting

Fuel Tank Assembly Several components go together to make up the fuel tank assembly: Fuel tank filler neck extension tube on the tank for filling the tank with fuel Spillback ball large ball in the fuel tank filler neck to prevent fuel from leaking out of the vehicle during fillups

Fuel Tank Assembly Filler cap Fuel tank baffles Fuel tank straps sealed to prevent the escape of fuel and fuel vapors from the tank cap is not vented to atmosphere Fuel tank baffles placed inside the tank to keep fuel from sloshing Fuel tank straps used to secure the tank to the vehicle

Fuel Tank Assembly

Tank Pickup-Sending Unit Extends down into the tank to draw fuel and operate the fuel gauge Sending unit is a variable resistor resistance changes with changes in the fuel level controls the amount of current reaching the fuel gauge

Tank Pickup-Sending Unit “Sock” filter strains out debris in tank

Fuel Gauge Operation

Fuel Tank Pressure Sensor Used to monitor the fuel tank pressure in late-model vehicles equipped with OBD II systems Aids in the operation of the evaporative emissions control system

Fuel Lines and Hoses Carry fuel from the tank to the engine Fuel lines are made of strong double-wall steel tubing Fuel hoses are made of synthetic rubber needed where movement occurs between parts, such as between the frame and the engine

Fuel Lines and Hoses Will cover in more detail in chapter 43 Fuel and emission control lines

Fuel supply line, fuel return line, and fuel vapor line are shown Fuel Lines and Hoses Fuel supply line, fuel return line, and fuel vapor line are shown

Fuel Return System Most fuel injected vehicles use a fuel return system to cool fuel and prevent vapor lock Fuel return line carries excess fuel back to the tank keeps cool fuel constantly flowing through the system

Returnless Fuel Injection Systems Some late-model vehicles do not have fuel return lines These vehicles use a pressure regulator mounted on the electric fuel pump assembly (in the fuel tank) When system pressure exceeds specifications, the regulator routes fuel back to the tank

Fuel Filters Used to stop contaminants such as rust, water, and dirt from entering the fuel lines, hoses, throttle body, injectors, pressure regulator or an other part that could be damaged “Sock” filter on the tank pickup tube is used to filter out debris Second filter is usually located in the main fuel line

Variations of Fuel Filters

Vapor Lock Problem created when bubbles in overheated fuel reduce or stop fuel flow Fuel boils, forming bubbles that displace liquid fuel Fuel bubbles reduce fuel pump output, causing engine performance problems Caused by high underhood temperatures and low fuel pressures

Vapor Lock

Fuel Pumps There are two basic types of fuel pumps: mechanical fuel pump electric fuel pump

Mechanical Fuel Pump Powered by an eccentric on the engine camshaft Bolts to the side of the engine block Used on carbureted gasoline engines

Electric Fuel Pump Produces fuel pressure and flow for the fuel metering section of a fuel system Located inside the fuel tank or in the fuel line between the tank and the engine A few systems use a pump in the tank and a second pump in the line to further increase fuel pressure

In-Tank Electric Fuel Pumps

Electric Fuel Pump Advantages Produces almost instant pressure Produces smoother flow than a mechanical pump Vapor lock is less likely because the pump is located away from the engine and pressurizes all the fuel lines that are near engine heat high pressure increases the boiling point of fuel

Electric Pump Circuit In this circuit, if the oil pressure drops too low, the switch shuts off the fuel pump