1. Subsystems of EFI
Chapter Lesson 2

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

3. Systems Overview

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

5. Fuel Delivery System

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

7. 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

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

9. 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

10. 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

11. Air Induction System

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

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

14. Electronic Control Module
Commonly mounted behind the instrument panel

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

16. 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

17. Signals air-fuel mixture
Oxygen Sensor
Signals air-fuel mixture

18. 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

19. Oxygen Sensor Construction

20. 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

21. 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

22. Information Flow
Open Loop
Closed Loop

23. 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

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

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

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

27. 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

28. Throttle Position Sensor
Variable resistor signals throttle position

29. 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

30. 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

31. Airflow Sensor Operation
This airflow sensor operates a variable resistor

32. 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

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

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

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

36. 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

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