Fuel Delivery Systems

Objectives (1 of 3)

• Explain the purpose of the fuel delivery system.

• List the commonly used components of the fuel delivery system.

• Explain how expansion, contraction, and overflow are controlled in the fuel tank.

Objectives (2 of 3)

• Explain the purpose of the check valves used in the fuel delivery system.

• Describe the function of the rollover valve.• Detail the emission controls associated

with the fuel delivery system.• Describe the operation of the electric fuel

pump.

Objectives (3 of 3)

• Explain how the pressure regulator operates.

• Explain the differences between return type and returnless fuel systems.

• Describe the types of materials and fittings used in common fuel lines.

• Detail the function of the intake manifold.

• Explain typical fuel pump circuit operation.

Introduction

• The fuel delivery system is responsible for: – Storing and delivering fuel to the engine– Controlling emissions from evaporating fuel– Filtering fuel

Fuel Tank

• Can be made of steel, aluminum, or plastic

• Contains baffles to prevent fuel slosh

• Must contend with expansion, contraction, and overflow

• Must control fuel evaporation

Rollover Valve

• Prevents leakage from the gasoline supply or vent line in case of a roll-over accident

• Mandated in 1976

On-board Refueling Vapor Recovery

• Large amounts of hydrocarbon emissions occur when a vehicle is refueled.

• Beginning in 1998, there was a phase-in of regulations to control the release of hydrocarbons (raw fuel vapors).– See the text for descriptions of systems in

use.

Fuel Pumps

• Most modern vehicles utilize an electric fuel pump.– Supplies a constant fuel pressure– Less prone to vapor lock than a

mechanical pump– Delivers fuel pressure high enough for fuel

injection

Reservoir Chamber

• The chamber prevents the fuel pump from losing its prime, especially when the level is low and the vehicle is maneuvering.

Pressure Relief Valve

• The relief valve prevents excessive fuel pressure from damaging components in case the fuel line is restricted.

• Pressure relief occurs at about 120 pounds.

One-way Check Valve

• This valve prevents fuel from running back to the tank when the pump is off.

• This fuel trapped in the line helps promote faster starts.

Return Line Check Valve

• This valve prevents fuel from running from the tank into the return line in a roll-over accident.

Fuel Filters

• A typical fuel injection system has two filters and a screen.– Strainer filter inside the fuel tank for large

debris– Main fuel filter– Fine screen located at each injector port

Fuel Lines

• All systems have a pressurized fuel delivery system, some have a non-pressurized return system.

• They can be made from metal tubing, flexible nylon, or synthetic rubber.

Fuel Line Connections

• Fuel lines are connected by utilizing:– Banjo fittings– Quick-connects– Compression fittings– Double-flare fittings

Fuel Rail

• The fuel rail connects directly to the injectors.

• It is either mounted on intake, or as a part of the intake.

Fuel Pressure Regulation

• The fuel pump is capable of delivering more pressure than needed.

• A fuel pressure regulator keeps fuel pump pressure constant.

Return-type Systems

• The pressure regulator is mounted on the fuel rail.

• Fuel not needed is returned to the tank via the return line.

• Intake manifold vacuum is applied to the regulator to sense engine load.

Returnless-type Systems

• Returnless fuel systems are becoming more common.

• The major advantages are:– Lower fuel temperature

• Fuel is not returned from hot engine to tank.

• Fuel only goes through the filter once.

Intake Manifolds

• Intake manifold design has changed over the years.

• Carburetor and throttle body manifolds carried the air/fuel mixture to the cylinders.

• Port fuel injected intakes carry only air, and are not heated by crossover exhaust.

Electric Fuel Pump Circuits

• Most electric fuel pumps use a PCM-controlled relay.

• Most are turned on at key on for a short time for a “prime pulse.”

• The pump will shut down after prime if the PCM does not see engine rpm.