EFI Flashcards
What does EFI stand for?
Electronic Fuel Injection
How does EFI function? (steps)
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
What are the 3 main types of Fuel Injection?
Throttle Body Injection (TBI)
Multi-Port Injection
Direct Injection (GDI)
Where is the fuel injector in MULTIPORT injection?
Multiport - the injector is behind the valve - max airflow
Where is the fuel injector in DIRECT injection?
Direct - the injector is in the combustion chamber
Where is the fuel injector in THROTTLE BODY injection (TBI)?
Uses 1 or 2 injectors mounted on top of the throttle butterfly
What is the most common form of fuel injection today?
Multiport injection is seen in most modern vehicles today with direct injection (GDI) becoming more popular
What is some of the information provided to the PCM via sensors?
-engine speed
-throttle position
-accelerator pedal position
-coolant temperature
-air temperature
-engine load
-knock (detonation
What sensor provides engine speed, measured in RPM, to the PCM?
The Crankshaft Position Sensor
What is a tone ring, and what is its function?
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.
What is the function of the camshaft position sensor?
Used by the PCM to determine when to:
- Fire the spark plugs
- Trigger the fuel injector
- Alter valve timing
What are the two types of camshaft/crankshaft position sensor?
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.
True or False: Throttle Position Sensor (TPS) is a variable resistor
True! TPS reports to the PCM the throttle’s current position
What are typical return voltage ranges for the different stages of the throttle position sensor?
- idle ≈ 0.5 volt
- ½ throttle ≈ 2.5 volts
- wide open throttle ≈ 4.5 volts
How many volts are sent as a signal from the PCM (Powertrain Control Module) to the TPS (Throttle Position Sensor)?
5 volts
Both coolant and engine temperature sensors are what type of sensor?
Thermistors - temperature sensitive resistors
How does the PCM use data from the engine temp sensor and the coolant temp sensor?
- more fuel if air or coolant temperatures drop
- less fuel as the engine warms up
Idling at a red light, is engine vacuum high or low? Why?
High engine vacuum:
Engine load is light
-RPMs low (slow pistons)
Throttle position is nearly closed
-Manifold pressure is low
4x4 going steep uphill, is engine vacuum high or low? Why?
Low engine vacuum:
Engine load is high
-RPMs high (fast pistons)
Throttle position is nearly all the way open
-Manifold pressure is high
What are the two factors that dictate intake manifold pressure?
Throttle position & piston speed
What is the MAP sensor and what is it responsible for?
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
What is the MAF sensor and what is it responsible for?
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
What is detonation, and what can cause it?
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
What does the knock sensor do?
Detects detonation & PCM can then respond by changing when spark occurs to combat detonation
What are the two types of sensors that provide feedback to the PCM?
1) Oxygen Sensor (O2 Sensor)
2) Air fuel ratio sensor
Where are oxygen and air-fuel ratio sensors located?
Are located downstream to the engine in the exhaust system
What do the oxygen and air-fuel ratio sensors measure?
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
How does the “Input → Process → Output → Feedback” system work in engine management?
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
What does the O2 sensor do in engine management?
The O2 sensor monitors the air-fuel mixture (AFM) and tells the PCM if it is rich or lean
What is the ideal air-fuel ratio (AFR) for a warmed-up engine under moderate throttle?
HINT: Atmospheric pressure
14.7:1 (14.7 parts air to 1 part fuel by weight).
14.7 lbs per in is atmospheric pressure
How does the air-fuel ratio change under different conditions? (Cold, Cruising, Downhill)
Cold engine: As rich as 12:1
Cruising (optimal): 14.7:1
Downhill: As lean as 18:1
How does the O2 sensor determine if the air-fuel mixture is rich or lean?
The O2 sensor compares the oxygen in the atmosphere to the oxygen remaining in the exhaust gases
What voltage does the O2 sensor produce when the air-fuel mixture is at the ideal ratio (14.7:1)?
≈0.45 volts
What voltage does the O2 sensor produce when the mixture is lean vs rich?
Lean: 0.1 – 0.4 volts
Rich: 0.6 – 1.0 volts
What do AFR (Air-Fuel-Ratio) sensors do in engine management? - And how does the PCM respond?
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.
How does the PCM control fuel delivery in an EFI system?
The PCM analyzes input sensor data and adjusts fuel delivery by varying how long the injector stays open
What is injector on-time called, and how is it measured?
Injector on-time is called pulse width, measured in milliseconds
How does the PCM control idle speed in a traditional cable-operated throttle system?
Using an Idle Air Control (IAC) motor
What component controls the throttle plate in an Electronic Throttle Control (ETC) system?
A DC servo motor opens and closes the throttle plate
What is Electronic Throttle Control (ETC), aka “drive-by-wire”?
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
