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