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Fuel Injection Fundamentals

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Presentation on theme: "Fuel Injection Fundamentals"— Presentation transcript:

1 Fuel Injection Fundamentals

2 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

3 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)

4 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

5 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.

6 Indirect Injection Sprays fuel into the engine intake manifold Most gasoline injection systems are indirect

7 Direct Injection Forces fuel into the engine combustion chamber All Diesel injection systems are the direct type

8 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)

9 Electronic Fuel Injection Four Subsystems
Fuel Delivery: Electric fuel pump Fuel filter Pressure regulator Fuel injectors Connecting lines and hoses

10 Air Induction System Consists of an Air filter Throttle valve Sensors
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

11 Questions What are the two gasoline fuel injection systems ?
What are the two ways fuel is injected into the combustion chamber (hint all diesel are this way)? What are the injector opening times? Name the parts that make up the Fuel delivery system?

12 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

13 Inputs /Outputs Inputs Outputs Oxygen sensor
Engine coolant temp sensor Throttle position sensor M.A.P Knock sensor Fuel pump relay EGR solenoid Fuel injectors Idle air control (I.A.C.)motor

14 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

15 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

16 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

17 Open Loop/Closed Loop Open Loop Closed Loop
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. 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

18 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 High PSI (low intake vacuum) indicates high load requiring a rich mixture Low manifold vacuum indicates very little load requiring a lean mixture sensor varies resistance with engine load

19 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

20 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 Cold the sensor provides low resistance high current flow the e.c.m would richen the mixture like a choke on a carb.

21 Questions? What is an engine sensor? What does P.C.M. stand for?
What job does an O2 sensor perform? What is open loop? What does M.A.P sensor stand for

22 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 Uses a heated wire element which changes the resistance of the reference voltage

23 Knock Sensor Piezoelectric sensor that detects engine pinging, preignition or detonation so the computer can retard timing

24 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

25 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

26 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

27 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

28 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

29 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

30 Questions What are the two electrical signals sensors produce?
How does a knock sensor work? What does a crankshaft position sensor do? What does T.B.I stand for?

31 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

32 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

33 Multi-port Throttle Body
The assemble contains the throttle plates, throttle position sensor Its main function is to control airflow into the engine

34 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

35 E.F.I. Troubleshooting Reading O2 sensor Normally O2 sensors are designed to last 80,000km however, it’s life can be shortened by contamination

36 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

37 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

38 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

39 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

40 O.B.D Systems O.B.D. 1 Early on board diagnostic system could only check a limited number of items 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

41 Questions What is Multiport injection?
What controls the fuel regulator on multiport injection? What two tools can we use to check fuel injectors? What are the OBD systems on vehicles?

42 Carburetor Theory

43 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

44 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

45 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

46 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

47 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 start 16:1 idling 15:1 part throttle 13:1 full acceleration 18:1 cruising speeds There are 7 basic carb. circuits

48 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

49 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

50 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

51 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

52 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

53 Full Power Circuit Enriches the high speed circuit when needed Power 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

54 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

55 Circuit Acronym F float Circuit I Idle circuit L Low speed M Main metering P Power circuit A Acceleration circuit C Choke circuit

56 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

57 Secondary Consists of the components or circuits that function under high engine power output conditions They only function when more power is needed

58 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

59 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.

60 Small Engine Carburetors

61 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

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