It uses pressure from an electric fuel pump to spray fuel into the engine’s intake manifold Unlike...
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Transcript of It uses pressure from an electric fuel pump to spray fuel into the engine’s intake manifold Unlike...
Fuel Injection Fundamentals
Gasoline Injection
It uses pressure from an electric fuel pump to spray fuel into the engine’s intake manifold
Unlike a carburetor Pressure not engine vacuum is used to feed the engine
This makes it very efficient
Gasoline Injection Advantages
Improved atomization (fuel broken into finer mist)
Better fuel distribution to each cylinder Smoother idle (can use a leaner mixture) Lower emissions (Air fuel ratio) Increased engine power (precise metering)
Injection Classifications
Throttle Body Has an injector
nozzles in a throttle body assembly on top of the engine
Fuel is sprayed
into the top center of the intake manifold
Multiport Injection
Has fuel injectors in the intake ports (air/fuel runners)
Gasoline is sprayed
into each intake port, towards each intake valve
Controls the air fuel mixture more precisely than T.B.
Indirect Injection
Sprays fuel into the engine intake manifold
Most gasoline injection systems are indirect
Direct Injection
Forces fuel into the engine combustion chamber
All Diesel injection systems are the direct type
Injector Opening Times
Simultaneous Injection : Means all of the injectors open at the
same time
Sequential injection: means that the injectors open one after another
Group Injection: has several but not all
of the injectors opening at the same time( V8 might have 4 injectors open at one time)
Electronic Fuel Injection Four Subsystems
Fuel Delivery:1. Electric fuel pump2. Fuel filter3. Pressure regulator4. Fuel injectors5. Connecting lines
and hoses
Air Induction System
Consists of an 1. Air filter2. Throttle valve3. Sensors4. Connecting duct work Air enters the duct
work The air filter traps particles it’s then routed to the
throttle body
The throttle body (multiport injection )
The air goes past the throttle plate and flows into the intake runners
The runners route the air into each cylinder head intake port
Questions
1. What are the two gasoline fuel injection systems ?
2. What are the two ways fuel is injected into the combustion chamber (hint all diesel are this way)?
3. What are the injector opening times?
4. Name the parts that make up the Fuel delivery system?
Sensor System
An EFI sensor system monitors engine operating conditions and reports this information to the engine control module
An engine sensor is an electrical device that changes circuit resistance or voltage with a change in a condition such as temperature, pressure or position
Inputs /Outputs
INPUTS OUTPUTS
1. Oxygen sensor2. Engine coolant temp
sensor3. Throttle position
sensor4. M.A.P5. Knock sensor
1. Fuel pump relay2. EGR solenoid3. Fuel injectors4. Idle air control
(I.A.C.)motor
P.C.M / E.C.M
Power train Control Module is the brain of an electronic fuel injection system it’s a preprogrammed microcomputer.
Input sensors feed information to the P.C.M. the P.C.M. uses this data to operate the Output sensors
Oxygen Sensor
It measures the oxygen content in the engine’s exhaust system as a means of checking combustion efficiency
Vehicles that are OBD 2 uses at least two O2 sensors Pre and Post catalytic converter
O2 Sensors
The voltage output (or resistance) of the 02 varies with changes in the oxygen content of the exhaust
Lean mixture makes the sensor output voltage decrease e.g. .1 volt
A decrease in oxygen from a rich mixture causes the sensor output to increase e.g. .9 Volt
Open Loop/Closed Loop
OPEN LOOP CLOSED LOOP
The P.C.M. does not use engine exhaust gas content as a main indicator of the air/fuel mixture
Instead the system operates on information stored in the P.C.M
The computer is using information from the oxygen sensor and other sensors
This information forms an imaginary loop from the P.C.M. to the fuel system to the exhaust system and back to the P.C.M.
M.A.P. Sensor
Manifold absolute pressure sensor it measures the pressure or vacuum inside the engine intake manifold
Manifold pressure is a good indicator of engine load
Throttle Position Sensor
T.P. sensor is a variable resistor connected to the throttle plate shaft
When the throttle opens or closes, the sensor changes resistance and signals the computer
Engine Temperature Sensor
Monitors the operating temp. of the engine
Its mounted so it is exposed to engine coolant
The P.C.M. uses this information to adjust air/fuel ratio
Questions?
1. What is an engine sensor?
2. What does P.C.M. stand for?
3. What job does an O2 sensor perform?
4. What is open loop?
5. What does M.A.P sensor stand for
Mass Airflow Sensor
Used to measure the amount of outside air entering the engine
This helps the E.C.M determine how much fuel is needed
Knock Sensor
Piezoelectric sensor that detects engine pinging, preignition or detonation so the computer can retard timing
Crankshaft Position Sensor
Used to detect engine speed
It allows the ECM
to change injector timing and duration with changes in engine RPM
Higher engine RPM more fuel
Sensor Signals
Digital signal Are on /off signals
An example of a sensor providing a digital signal is the crank shaft position
Voltage goes from max. to min. like a light switch
Sensor Signals
Analog Signal Changes in
strength to let the computer know about change in a condition
e.g. Coolant temp sensor it’s a variable resistance
Throttle Body Injection
The injector sprays fuel into the top of the throttle body air horn
The fuel spray mixes with the incoming air
The mixture is then pulled into the engine by intake manifold vacuum
T.B.I. Assembly
Typically consists of: Throttle body
housing-this is the metal casting that holds the subassemblies
Fuel Injector- a solenoid operated fuel valve
Fuel Regulator-a spring loaded bypass valve that maintains constant pressure at the injector
Throttle position sensor a variable resistor that reads throttle plate position
TBI Fuel Pressure Regulator
Consists of a fuel valve, diaphragm, and spring
When fuel pressure is low (starting engine) The spring holds the fuel valve closed. This causes pressure to build
When a preset pressure is reached the spring is over come
Questions
1. What are the two electrical signals sensors produce?
2. How does a knock sensor work?
3. What does a crankshaft position sensor do?
4. What does T.B.I stand for?
I.A.C. Motor
Idle Air Control Valve It’s a solenoid or a
stepper motor controlling the air bypass around the throttle plates
Its computer controlled Its used on both multiport and TBI injection
Multi Port Fuel injection
Uses a computer, engine sensors and one solenoid injector for each cylinder
This is the most common system used on late model vehicles
Multi-port Throttle Body
The assemble contains the throttle plates, throttle position sensor
Its main function is to control airflow into the engine
Fuel Pressure Regulator on Multi-port
Is mounted in the fuel rail after the injectors performs the same function as Throttle body injection
It differs by using engine vacuum to control it rather then spring tension
E.F.I. TroubleshootingReading O2 sensor Normally O2
sensors are designed to last 80,000km however, it’s life can be shortened by contamination
Injector Tests
Using a Noid light to check the harness side of the injector
They are designed
to check for normal digital current pulses
To test the injector do a balance test
Injector Spray Patterns
Injector 1. FAIR - but weak
Injector 2. BAD - split spray pattern
Injector 3. BAD - split spray pattern
Injector 4. BAD - jetting on left side
Injector 5. GOOD
Injector 6. BAD - feathering at top of spray
Scan Tool
Used to communicate and retrieve trouble codes from the vehicles computer
It also displays circuit and sensor values, run tests and give helpful hints for finding problems
On Board Diagnostic System
If the onboard computer finds any abnormal values it will store a trouble code and light a malfunction indicator light on the instrument panel
Some vehicles can have 6 more computers
O.B.D Systems
O.B.D. 1 Early on board diagnostic system could only check a limited number of items 1986-1995
O.B.D 2 designed to more efficiently monitor the condition uses greater processing speed more memory and more complex tasks 1996-present
C.A.N. O.B.D Controller Area Networking all 2008 and newer vehicles
CAN-equipped vehicle is
shared over a serial data bus. The bus is the circuit that carries all the electronic chatter between modules
Questions
1. What is Multiport injection?
2. What controls the fuel regulator on multiport injection?
3. What two tools can we use to check fuel injectors?
4. What are the OBD systems on vehicles?
Carburetor Theory
Carburetor Basics
A carburetor is basically a device that mixes air and fuel in the correct proportions (amounts) for efficient combustion
When the engine is running the intake stroke creates suction in the intake manifold
Air rushes through the carb. were fuel is mixed with it
Carburetor Parts
Body-Is cast metal housing for the components It has cast and drilled passages for air and fuel
Air Horn-also called barrel routes outside air into the engine intake manifold
Carburetor Parts
Throttle Valve-is a butterfly valve located in the air horn when its closed it restricts air flow into the engine
Venturi- produces suction to pull fuel out of the main discharge tube The narrow air way increases air velocity
Main Discharge tube-also called main fuel nozzle it’s passages in the main body that connects the fuel bowl to the venturi
Fuel bowl-holds a supply of fuel that is not under fuel pump pressure
Carburetor Circuit
Is a network of passages and related parts that help control the air/fuel ratio under a specific engine operating condition
Each circuit supplies a predetermined air/fuel mixture as the temperature, speed and engine load change
Must be capable of providing varying air/fuel ratios:
8:1 cold start16:1 idling15:1 part throttle13:1 full acceleration18:1 cruising speeds
There are 7 basic carb. circuits
Float System
Must maintain the correct level of fuel in the carburetor bowl
The float system prevents the fuel pump from forcing too much fuel in the bowl
The bowl is also vented to prevent psi and vacuum buildup
Needle and seat works with the float to control the flow
Idle System
Provides the engine’s air/fuel mixture at speeds below 800 RPM or 20 KM/h
The throttle is almost closed there is no venturi action instead high intake vacuum below the throttle plates feed fuel into the barrel
Part Throttle Circuit
Feeds more fuel into the air horn when the throttle plates are partially open. Functions above 800 RPM
Without this circuit the mixture would become too lean off idle
Acceleration Circuit
Provides extra fuel when changing from the idle circuit to high speed circuit
The acceleration circuit squirts a stream of fuel into the barrel when the accelerator is pressed
Main Metering System Supplies the engine
air/fuel at cruising speeds It begins to function when the throttle plates are open enough for venturi action
Provides the most efficient fuel/air ratio
The jet hole size determines how much fuel flows through the circuit
Full Power CircuitEnriches the high speed
circuit when neededPower valve :when the engine is at cruise
speed the manifold vacuum is high the vacuum acts on the diaphragm and pulls the valve closed
When the throttle plates are swung open engine manifold vacuum drops off the spring in the power valve opens and fuel flows
Choke Circuit
Designed to provide an extremely rich air/fuel mixture to aid in cold starts
Is a butterfly valve located at the top of the carburetor air horn when its closed it blocks normal air flow causing high intake vacuum to form below the choke plate pulling fuel from the main discharge tube
Circuit Acronym
F float CircuitI Idle circuitL Low speedM Main meteringP Power circuitA Acceleration circuitC Choke circuit
Primary
Are the components that operate under normal driving conditions
In a 4 barrel carburetor the primary consists of the 2 front throttle plates and related components
Secondary
Consists of the components or circuits that function under high engine power output conditions
They only function when more power is needed
Carburetor Size
Generally carburetor Size is stated in CFM (cubic feet of air per minute)
This is the amount of air that can flow through the carburetor at wide open throttle
Variable Venturi• A slide-type, has a cylinder-shaped slide that moves in
and out of the air horn to help control fuel and airflow.• The piston sliding in and out regulates the size of the
venturi. These are commonly used on motorcycles.
Small Engine Carburetors
Summary
A carburetor is basically a device for mixing air and fuel in correct amounts
The float system must maintain the correct level in the bowl
Low speed circuit feeds more fuel into the barrel when the throttle plates are partially open
The main metering circuit supplies the engine’s air/fuel mixture at normal cruising speeds
The power circuit provides a means of enriching the fuel mixture for high speed
The choke circuit is designed to supply an extremely rich air/fuel ratio to aid in cold starts