Subsystems of EFI Chapter 22 Lesson 2

Electronic Fuel Injection (EFI) EFI system can be divided into four subsystems: fuel delivery system air induction system sensor system computer control system

Systems Overview

Fuel Delivery System Components electric fuel pump fuel filter fuel pressure regulator injectors

Fuel Delivery System

Electric Fuel Pump Draws gasoline out of the tank Forces it to the fuel rail

Fuel Pressure Regulator Controls the pressure entering the injector(s) Returns excess fuel to the tank Vacuum may be ported into the regulator lower pressure at idle increasing pressure at higher load

Fuel Pressure Regulator Low vacuum, high load High vacuum, low load

Injectors Solenoid-operated fuel valve Electrical terminals Armature Injector body Needle valve Fuel inlet Inlet screen Return spring Coil windings Spray mist Solenoid-operated fuel valve When current flows, magnetism attracts the armature to open the injector valve

Air Induction System Air filter Throttle valve(s) Sensors Ducts traps dust and debris Throttle valve(s) controls airflow through the throttle body Sensors sense airflow and throttle position Ducts route clean air to the throttle body

Air Induction System

Sensor System Inputs to the control module Signal the following operating conditions: temperature position pressure or vacuum speed

Computer Control System Uses data from the sensors to control fuel injectors Wiring harness connects computer to sensors and injectors

Electronic Control Module Commonly mounted behind the instrument panel

Engine Sensors Oxygen (O2) Manifold absolute pressure (MAP) Throttle position (TP) Engine coolant temperature(ECT) Airflow Intake air temperature (IAT) Crankshaft position (CKP)

Oxygen Sensor Measures oxygen content in the exhaust In OBD I vehicles, the sensor is threaded into the exhaust manifold before the catalytic converter OBD II equipped vehicles also use at least two oxygen sensors one before and one after each catalytic converter the sensor located after the converter monitors catalyst efficiency

Signals air-fuel mixture Oxygen Sensor Signals air-fuel mixture

Oxygen Sensor Operation Increase in exhaust oxygen from lean mixture causes oxygen sensor voltage to decrease Decrease in exhaust oxygen from rich mixture causes oxygen sensor voltage to increase

Oxygen Sensor Construction

Open Loop Injection system does not use exhaust gas oxygen as an indicator of air-fuel mixture Operation is from information stored in the computer Cold engines operate in open loop

Closed Loop Computer uses information from the oxygen sensor as a main input for air-fuel mixture control Normally, hot engines operate in closed loop

Information Flow Open Loop Closed Loop

MAP Sensor Senses engine load by measuring pressure, or vacuum, inside the intake manifold High pressure (low vacuum) indicates high load Low pressure (high vacuum) indicates low load

Often mounted on the engine or in the engine compartment MAP Sensor Often mounted on the engine or in the engine compartment

Piezo-resistor chip converts pressure change into resistance change MAP Sensor Theory Piezo-resistor chip converts pressure change into resistance change

Manifold vacuum flexes the chip, altering its resistance MAP Sensor Side View Manifold vacuum flexes the chip, altering its resistance

Throttle Position Sensor Senses throttle position Variable resistor connected to the throttle plate As the throttle opens or closes, sensor resistance changes, signaling throttle position

Throttle Position Sensor Variable resistor signals throttle position

Engine Coolant Temperature Sensor Senses engine coolant temperature At low temperatures, sensor resistance may be high computer will richen mixture At high temperatures, sensor resistance may be low computer will deliver leaner mixture

Airflow Sensor Measures amount of air entering engine Air flap or door operates a variable resistor Airflow opens the flap, changing position of the variable resistor and changing the signal voltage to the computer

Airflow Sensor Operation This airflow sensor operates a variable resistor

Intake Air Temperature Sensor Measures the temperature of the air entering the engine Air temperature affects air density Cooler air is more dense, requiring more fuel Helps the computer compensate for changes in outside air temperature

Crankshaft Position Sensor Detects engine speed and position Information is used by computer for fuel injection operation

Digital Signals Signal is on or off Voltage goes from maximum to minimum instantly Crankshaft position sensor output may be a digital signal

Analog Signals Signal varies in voltage or strength May be produced by change in resistance of a sensor as temperature, pressure, or position changes

Injector Pulse Width Pulse width is the amount of time an injector is energized At wide open throttle, computer lengthens injector pulse to richen mixture At low load, computer shortens pulse width

Pulse width controls the amount of fuel injected Injector Pulse Width Pulse width controls the amount of fuel injected