Analysis of Spark Ignition Engine
Management System
James Bower
Josh Duke
Casey Fisher
Engine Management System
Engine Management
System Basics
Advantages of EFI
Future Trends
The Brains of the Car
Electronic Control Unit or ECU
Small computer connected directly to engine
Monitors engine parameters through the use of sensors
Manages throttle control, ignition, fuel injection, and
power
Fuel Mapping
Through the use of the ECU data and computer programs the
engine can be mapped depending on speed and load of the
engine.
Fuel and timing settings can be adjusted using these maps to
achieve maximum performance from the engine.
Crank Sensor
Determines speed of
engine
Consists of toothed wheel
and an inductive pickup
Sensor pulses and
creates a magnetic field
Depending on location of
wheel, changes magnetic
field strength
From magnetic strength
the ECU can tell the
exact crank position and
speed
Throttle Position Sensor
Determines the load on the engine
Two types:
1) Electronic accelerator pedal

Senses force applied to pedal and opens throttle body
accordingly
2) Direct linkage

Uses a linkage between pedal and throttle
Mass Airflow Sensor
Current setup uses hot
wire method
Heated wire placed in
venturi section and air
flows over wire and cools
Measures current
required to keep at a
constant temperature
ECU converts voltage
drops into mass airflow
Lambda Sensor (Oxygen Sensor)
One of the most important components of the engine
management system
This device is extremely important in fuel conservation and
emissions control
The amount of oxygen present in the exhaust stream is a direct
result of the air/fuel ratio
Oxygen Sensor - How it Works
Sensor consists of two
electrodes, one exposed to air
and the other exposed to the
exhaust gases
Difference in partial pressures
of oxygen produces a voltage
The ECU reads how much fuel
should be injected based on
the voltage
Rich mixtures contain little free
oxygen
Lean mixtures contain
considerable free oxygen
Temperature Sensor
Temperatures measured
with a sensor known as a
thermistor
A thermistor is a resistor
made of a semiconductor
material whose electrical
resistance changes with
temperature
Pressure Sensor
Used to monitor intake
manifold and ambient
pressures
Measured by semiconducting silicon
diaphragm that separates
two chambers
Pressure change causes
diaphragm to flex
When diaphragm flexes
cause resistance of
material to change
ECU monitors voltage
change
Knock Sensor
Sensors alert ECU
when vibrations are
detected in the
cylinder
Knock sensors
contain a piezoelectric
crystal
Crystal produces an
electric signal when
subjected to physical
stress due to engine
knock.
ECU responds by
retarding or advancing
ignition time
EFI Systems
Advantages
Improved fuel distribution
Engine power increases by average of 10 percent
Faster acceleration resulting from direct delivery of
fuel to the cylinder
Leaner air/fuel ratios
 better fuel economy
 reduced exhaust emissions
Decreased engine knock
Elimination of inlet manifold backfiring and icing
EFI Systems
Disadvantages
Cost
More vulnerable than carburetors
 Require clean fuel and air to operate correctly
 Dirt could cause significant damage to system
Future Trends
Replacement of mechanical and hydraulic linkages with
purely electrical systems
Electronically controlled valve systems



Faster opening and closing times
Minimal impact forces
Optimized fuel consumption and engine power
Implementation of direct fuel injectors


Increased fuel efficiency
Reduced emissions
Drive-by-wire chassis





Electronically controlled breaking, steering, and shifting
Shortened braking distance
Improved vehicle stability
Lower maintenance costs
Potential for remote diagnosis and maintenance
Conclusion
The electronic fuel management system of
today’s engines is a revolutionary design
that works to maximize engine performance
while reducing emissions. This new
technology allows for changes in the engine
while it is running to achieve peak
performance. These systems will only
continue to improve as technology
advances.