EFI

Question 1

What does EFI stand for?

Answer 1

Electronic Fuel Injection

Question 2

How does EFI function? (steps)

Answer 2

The PCM (Powertrain Control Module) reads via sensors to determine how much fuel the engine needs and turns on the fuel injector to spray fuel

1) Input: Sensors
2) Processing: PCM
3) Output:
- fuel quantity
- spark timing
- idle speed
- emission controls

Question 3

What are the 3 main types of Fuel Injection?

Answer 3

Throttle Body Injection (TBI)
Multi-Port Injection
Direct Injection (GDI)

Question 4

Where is the fuel injector in MULTIPORT injection?

Answer 4

Multiport - the injector is behind the valve - max airflow

Question 5

Where is the fuel injector in DIRECT injection?

Answer 5

Direct - the injector is in the combustion chamber

Question 6

Where is the fuel injector in THROTTLE BODY injection (TBI)?

Answer 6

Uses 1 or 2 injectors mounted on top of the throttle butterfly

Question 7

What is the most common form of fuel injection today?

Answer 7

Multiport injection is seen in most modern vehicles today with direct injection (GDI) becoming more popular

Question 8

What is some of the information provided to the PCM via sensors?

Answer 8

-engine speed
-throttle position
-accelerator pedal position
-coolant temperature
-air temperature
-engine load
-knock (detonation

Question 9

What sensor provides engine speed, measured in RPM, to the PCM?

Answer 9

The Crankshaft Position Sensor

Question 10

What is a tone ring, and what is its function?

Answer 10

A tone ring is a toothed wheel attached to a crankshaft or wheel hub. It works with a sensor to generate signals used by the PCM or ABS system to determine speed and position.

Question 11

What is the function of the camshaft position sensor?

Answer 11

Used by the PCM to determine when to:
- Fire the spark plugs
- Trigger the fuel injector
- Alter valve timing

Question 12

What are the two types of camshaft/crankshaft position sensor?

Answer 12

2-wire sensor
(Magnetic/Variable Reluctance Sensor):
- Does not require an external power source.
- Produces an AC voltage signal as the tone ring passes by.

3-wire sensor (Hall Effect Sensor):
- Requires an external power source (typically 5V from the PCM).
-Produces a digital on/off signal (square wave) using tone ring.

Question 13

True or False: Throttle Position Sensor (TPS) is a variable resistor

Answer 13

True! TPS reports to the PCM the throttle’s current position

Question 14

What are typical return voltage ranges for the different stages of the throttle position sensor?

Answer 14

• idle ≈ 0.5 volt
• ½ throttle ≈ 2.5 volts
• wide open throttle ≈ 4.5 volts

Question 15

How many volts are sent as a signal from the PCM (Powertrain Control Module) to the TPS (Throttle Position Sensor)?

Answer 15

5 volts

Question 16

Both coolant and engine temperature sensors are what type of sensor?

Answer 16

Thermistors - temperature sensitive resistors

Question 17

How does the PCM use data from the engine temp sensor and the coolant temp sensor?

Answer 17

• more fuel if air or coolant temperatures drop
• less fuel as the engine warms up

Question 18

Idling at a red light, is engine vacuum high or low? Why?

Answer 18

High engine vacuum:

Engine load is light
-RPMs low (slow pistons)
Throttle position is nearly closed
-Manifold pressure is low

Question 19

4x4 going steep uphill, is engine vacuum high or low? Why?

Answer 19

Low engine vacuum:

Engine load is high
-RPMs high (fast pistons)
Throttle position is nearly all the way open
-Manifold pressure is high

Question 20

What are the two factors that dictate intake manifold pressure?

Answer 20

Throttle position & piston speed

Question 21

What is the MAP sensor and what is it responsible for?

Answer 21

A manifold absolute pressure (MAP) sensor measures the pressure inside the intake manifold and sends that signal to the PCM as an indicator of engine load.

When engine load is heavy: The PCM increases fuel injection.

When engine load is light: The PCM decreases fuel injection

Question 22

What is the MAF sensor and what is it responsible for?

Answer 22

A Mass Air Flow (MAF) sensor measures the amount of air entering the engine to help determine engine load.

The MAF sensor accounts for:
-Air volume
-Air density
-Humidity level
-Air temperature* temp sensor is built in to the MAF

Question 23

What is detonation, and what can cause it?

Answer 23

When air-fuel mixture in the cylinder ignites prematurely or unevenly, creating shock waves.

Detonation can be caused by excessive heat in the combustion chamber, carbon build-up or low octane fuel.

also called knocking or pinging

Question 24

What does the knock sensor do?

Answer 24

Detects detonation & PCM can then respond by changing when spark occurs to combat detonation

Question 25

What are the two types of sensors that provide feedback to the PCM?

Answer 25

1) Oxygen Sensor (O2 Sensor) 2) Air fuel ratio sensor

Question 26

Where are oxygen and air-fuel ratio sensors located?

Answer 26

Are located downstream to the engine in the exhaust system

Question 27

What do the oxygen and air-fuel ratio sensors measure?

Answer 27

They measure how much oxygen is left in the exhaust gasses and tell the PCM if there was too much or too little oxygen to support burning of fuel

Question 28

How does the "Input → Process → Output → Feedback" system work in engine management?

Answer 28

Input: Sensors provide data to the PCM Process: The Powertrain Control Module (PCM) analyzes sensor data Output: The fuel injector delivers the precise amount of fuel Feedback: The Oxygen Sensor (O2) or Air-Fuel Ratio (AFR) Sensor sends exhaust data back to the PCM

Question 29

What does the O2 sensor do in engine management?

Answer 29

The O2 sensor monitors the air-fuel mixture (AFM) and tells the PCM if it is rich or lean

Question 30

What is the ideal air-fuel ratio (AFR) for a warmed-up engine under moderate throttle? HINT: Atmospheric pressure

Answer 30

14.7:1 (14.7 parts air to 1 part fuel by weight). 14.7 lbs per in is atmospheric pressure

Question 31

How does the air-fuel ratio change under different conditions? (Cold, Cruising, Downhill)

Answer 31

Cold engine: As rich as 12:1 Cruising (optimal): 14.7:1 Downhill: As lean as 18:1

Question 32

How does the O2 sensor determine if the air-fuel mixture is rich or lean?

Answer 32

The O2 sensor compares the oxygen in the atmosphere to the oxygen remaining in the exhaust gases

Question 33

What voltage does the O2 sensor produce when the air-fuel mixture is at the ideal ratio (14.7:1)?

Answer 33

≈0.45 volts

Question 34

What voltage does the O2 sensor produce when the mixture is lean vs rich?

Answer 34

Lean: 0.1 – 0.4 volts Rich: 0.6 – 1.0 volts

Question 35

What do AFR (Air-Fuel-Ratio) sensors do in engine management? - And how does the PCM respond?

Answer 35

AFR sensors “tell” the PCM how rich or lean the air-fuel mixture (AFM) is and the PCM adjusts the air-fuel mixture as needed based on AFR sensor feedback.

Question 36

How does the PCM control fuel delivery in an EFI system?

Answer 36

The PCM analyzes input sensor data and adjusts fuel delivery by varying how long the injector stays open

Question 37

What is injector on-time called, and how is it measured?

Answer 37

Injector on-time is called pulse width, measured in milliseconds

Question 38

How does the PCM control idle speed in a traditional cable-operated throttle system?

Answer 38

Using an Idle Air Control (IAC) motor

Question 39

What component controls the throttle plate in an Electronic Throttle Control (ETC) system?

Answer 39

A DC servo motor opens and closes the throttle plate

Question 40

What is Electronic Throttle Control (ETC), aka “drive-by-wire”?

Answer 40

The throttle cable is eliminated compared to cable actuated throttles, and the PCM controls airflow into the engine instead of the driver and a Pedal Position Sensor (PPS) is added