1. Electronic Fuel Injection
Chapter 30
Electronic Fuel Injection

2. Electronic Fuel Injection
The ideal fuel ratio is called stoichiometric
This means all of the fuel and oxygen are completely consumed during combustion
The ideal environment rarely exists
The FI system adjusts to changes for starting, maximum power, and maximum economy

3. Basic EFI The PCM must know the amount of air entering the engine
In MAP sensor systems, air flow is calculated based on intake manifold pressure and RPM – called a speed density system
MAF sensor systems directly measure incoming air flow

4. Basic EFI (Cont.)
During closed loop the PCM relies on input from sensors to adjust the air/fuel ratio
The PCM uses inputs and look-up tables in memory to determine the ideal mixture
During starting and wide-open throttle the system is in open loop

5. Open and Closed Loop

6. Fuel Injectors
Electromechanical devices that meters and atomize fuel

7. Fuel Injectors (Cont.)
The amount of fuel injected depends on fuel pressure and injector pulse width time
Typical pulse width is 1 – 10 ms at full load
Primary factors are load and engine temperature
Injector design and fuel additives help reduce injector tip deposits and clogging

8. Idle Speed Control
On non-ETC engines, idle speed controlled with bypass air

9. Idle Speed Control (Cont.)
The PCM increases or decreases idle air bypass depending on engine speed, temperature, and load
During cold starts, the PCM keeps idle speed high to raise catalytic converter temperature

10. Inputs Injector control based on sensor input
MAF sensors measure incoming air volume and density
MAP sensors detect changes in intake manifold pressure
O2 sensors monitor exhaust oxygen content
IAT sensors measure incoming air temperature
ECT sensors monitor engine coolant temperature

11. Mass Airflow Sensor

12. MAP Sensor

13. Inputs (Cont.) O2 sensors monitor exhaust oxygen content
IAT sensors measure incoming air temperature
ECT sensors monitor engine coolant temperature

14. IAT

15. ECT

16. Inputs (Cont.)
TP sensors are used to clarify load and operating conditions
CKP sensors monitor engine speed
CMP sensors used to synchronize injector firing
VSS is used to further define operating conditions

17. TP Sensor

18. VSS

19. Additional Input Information Sensors
Additional sensors are used to provide information regarding:
Detonation
Air conditioner operation
Gearshift lever position
Battery voltage
EGR valve position

20. Operational Modes
Starting
Run
Clear Flood
Acceleration
Deceleration

21. Knowledge Check
Describe why so many inputs are used to control the fuel injection system.
Multiple sensors are used so the PCM can provide the most accurate amount of fuel delivery possible for any given operating condition.

22. Starting Mode
Fuel pump activated for two seconds and after CKP reference received
Injector pulse width determined by:
ECT, MAF, IAT, and TP

23. Run Mode
Once a predetermined RPM is reached, system goes into open loop
Injector pulse width set by:
MAF or MAP, IAT, ECT, TP
Closed loop begins based on input from the ECT and O2 sensors

24. Closed Loop

25. Clear Flood Mode
If too much fuel is received, it must be pumped out of the cylinders
Fully depress accelerator pedal and crank engine
PCM detects wide open throttle and cranking RPM

26. Acceleration Mode Based on signals from TP and MAF or MAP
To compensate, the PCM increases injector pulse width
Once the PCM determines the vehicle is no longer accelerating, the system returns to run mode

27. Deceleration Mode
Inputs from MAF or MAP and TP used to determine deceleration
PCM reduces injector pulse width
Some systems completely shut the injector off during rapid deceleration

28. Fuel Trim
PCM constantly monitors HO2S or air-fuel ratio sensors in closed loop
Alters injector pulse width to provide the best driveability, economy, and emission control
Expressed as a percentage
Base pulse width is 0 percent

29. Fuel Trim

30. Fuel Trim (Cont.)
The system allows for short term (STFT) and long term (LTFT) changes
LTFT are changes to set a new pulse width

31. Knowledge Check
Technician A says positive fuel trim means the PCM is adding fuel beyond the base calculation. Technician B says excessive positive fuel trim indicates a lean exhaust condition. Who is correct?
Both Technicians A and B

32. Throttle Body Injection (TBI)
Used to move from carburetors to fuel injection
Use one or two injectors over the throttle plate
Not as efficient as port fuel injection
No longer in use
Fuel pressure typically 10 – 15 psi

34. Port Fuel Injection (PFI)
At least one injector per cylinder
Delivers fuel just outside combustion chamber
Allows for good atomization
Several different types used over years:
Multiport injection (MPI)
Sequential fuel injection (SFI)

36. Multi-Port Injection (MPI)
The injectors are arranged and fired together in groups or pairs
No longer in use
Fuel charge must wait for intake valve to open
MPI systems are commonly speed density systems

37. Sequential Fuel Injection (SFI)
Sequential Injection (SFI)
Each injector is fired individually just before the intake valve for that cylinder opens
Typically use MAF sensors
Injectors fire according to CKP

39. Throttle Body
Controls air entering the engine and vacuum in the intake
May contain a MAP sensor, IAC assembly, throttle plate(s), and TP sensor
Many throttle body bores and plates coated with a special coating to prevent carbon buildup

41. Fuel Delivery Injectors controlled separately by PCM
Fuel supplied to the injectors by the fuel rail
The rail may contain a pressure test port
V engines usually have left and right rails
Some engines use variable intake runners for high and low speed operation

42. Typical Fuel Rail

43. Pulsation Damper
Reduces pulsations caused by rapid opening and closing of injectors

44. Injector Control
Injector opening timed to occur before the intake valve opens
SFI engines require CKP and CMP input to fire each injector

45. Pressure Regulators
MPI injector tips are located in the intake manifold where constant changes in vacuum affect fuel delivery
The fuel pressure regulator adjusts fuel pressure to maintain a constant pressure drop for each injector

47. Returnless Systems
Most newer systems have the pressure regulator as part of the fuel sender/pump
Only the fuel needed by the engine is filtered and sent to the injectors

48. Throttle-by-Wire Systems
Offer improved driveability, fuel efficiency, and decreased emissions
The PCM controls a DC throttle plate motor based on input from accelerator position sensors
Redundant sensors and springs are used for safety and limp-in operation

50. Central Multi-Port Fuel Injection
Uses one central injector
Fuel is delivered to individual poppet nozzles
Fuel pressure is higher than most PFI systems
Poppet nozzles snap into lower intake
Each nozzle contains a check ball and spring
The nozzle opens when pressure exceeds 37 – 43 psi

53. Gasoline Direct-Injection Systems
Used for many years on diesel engines
Highly pressurized fuel is sprayed directly into the cylinders

54. Injectors Special injectors seal after fuel is sprayed
Fuel pressure is much higher than standard MPI systems
High voltage injector drivers also required
Fuel can be injected at any time

55. Gasoline Direct Injection (GDI) Features
Allows for very lean air/fuel mixtures
Increases volumetric efficiency
Uses very high fuel pressures (typically between 400 and 2000 psi)
System operates similarly to diesel injection systems

56. Typical GDI System

57. High Pressure Fuel Pump
Gas is delivered to the engine by an in-tank pump
A mechanical, high-pressure pump increases fuel pressure to between 435 to 1885 psi
Pressure regulated by input from fuel rail pressure sensor

58. Operational Modes Lean Burn Stoichiometric Full Power
Can run as high as 60:1
Stoichiometric
During medium load
Full Power
During heavy loads and hard acceleration

60. Compression Ratios
The ability to change air/fuel ratios eliminates spark knock, allowing higher compression ratios
Does not require higher octane fuel
Smaller fuel droplets cool the cylinder
Mixture burns more quickly
Less need for spark advance

61. Advantages of GDI Increased fuel economy High power output
Increases engine volumetric efficiency
Lowers engine thermal loss
Decreases emissions
Allows higher compression
Reduces most turbo lag when turbocharged

62. GDI plus SFI
Some engines use a combination of direct and indirect injection
Each cylinder has two injectors
PCM shuts off port injection when not needed
Both injectors operate during cold starts

64. Knowledge Check
Technician A says GDI systems use high-pressure mechanical pumps to deliver fuel to the injectors. Technician B says GDI systems also use PFI injectors. Who is correct?
Both Technicians A and B