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Fuel Injection System. Fuel Injection System. Uses pressure (not Vacuum) from an electrical pump to spray fuel into the intake manifold. Provides the engine with proper air-fuel ratio (14.7 : 1). Fuel Injection System. Advantages. Improved Atomization . Better fuel flow .

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fuel injection system2
Fuel Injection System
  • Uses pressure (not Vacuum) from an
  • electrical pump to spray fuel into the
  • intake manifold.
  • Provides the engine with proper
  • air-fuel ratio (14.7 : 1)
fuel injection system3
Fuel Injection System


  • Improved Atomization
  • Better fuel flow
  • Smoother idle
  • Improved fuel economy
  • Lower emissions
  • Better cold weather drivability
  • Increased engine power
  • Simpler
fuel injection system4
Fuel Injection System

Atmospheric Pressure

  • Pressure formed by the air
  • surrounding the earth.
  • Atmospheric pressure is 14.7psi
  • at sea level.
  • Any space with less than 14.7psi
  • at sea level has vacuum.
  • Engine acts as a vacuum pump,
  • producing vacuum in the intake
  • manifold.
fuel injection system5
Fuel Injection System

Engine Throttle Valve

  • Controls air flow and gasoline to power engine.
  • When butterfly valve is closed it restricts air-flow and the
  • resulting flow of fuel into the engine.
  • When accelerator is pressed, the air-flow is increased in the
  • intake manifold.
  • Engine sensors detect the resulting changes and increase fuel
  • flow through the injectors.
fuel injection system6
Fuel Injection System

Electronic Fuel Injection uses various engine sensors and control

module to regulate the opening and closing of injector valve.

  • Fuel delivery system
  • Air induction system
  • Sensor system
  • Computer control system
fuel delivery system
Fuel Delivery system
  • Electrical Fuel Pump draws fuel from
  • tank and forces it into the regulator.
  • Pressure Regulator controls the amount
  • of pressure that enters the injector and any
  • extra fuel is returned to the fuel tank.
  • Fuel Injector is simply a coil or solenoid
  • operated valve.
  • Spring pressure holds the injector closed.
  • When engaged, the injector sprays fuel
  • into the engine.

Injector Pulse Width indicates the time each

Injector is energized (Kept Open).

air induction system
Air Induction System
  • Air filter
  • Throttle valve
  • Sensors
  • Connecting ducts
sensor system
Sensor System
  • Monitors engine operating condition and reports this information
  • to ECM (computer).
  • Sensors are electrical devices that change resistance or voltage
  • with change in condition such as temperature, pressure and position.
computer control system
Computer Control System
  • Uses electrical data from the sensors to control the operation of
  • the fuel injectors.
  • Engine Control Module (ECM)- “Brain” of the electronic fuel
  • injection.
engine sensors
Engine Sensors

Oxygen Sensor measures the oxygen content in engine exhaust.

  • Mounted on the exhaust system before the
  • catalytic converter.
  • Voltage out-put of O2 sensor changes with
  • the change in oxygen content of exhaust.
  • Lean mixture decreases the voltage.
  • Rich mixture increases the voltage.
  • Signal is sent to ECM and the ECM changes the time that an injector
  • is open or close.
engine sensors12
Engine Sensors

Open Loop

  • When the electronic injection system doesn’t use the input from
  • the engine exhaust.
  • System operates on information stored in the computer (PROM).
  • Computer ignores the sensors when the engine is cold.

Closed Loop

  • Ones engine reaches the operating temperature, computer uses
  • information from oxygen sensor and the other sensors.
engine sensors13
Engine Sensors

Manifold Absolute Pressure Sensor (MAP)

  • Measures the pressure, or vacuum inside
  • the engine intake manifold.
  • Manifold pressure = Engine load
  • High pressure (low intake vacuum) =
  • High load = Rich mixture
  • Low pressure (high intake vacuum) =
  • Little load = Lean mixture
  • Computer senses the change in resistance
  • and alters the fuel mixture.
engine sensors14
Engine Sensors

Throttle Position Sensor (TPS)

  • Variable resister connected to the
  • throttle plate.
  • Change in throttle angle =
  • change in resistance.
  • Based on the resistance, ECM
  • richens or leans the mixture.
engine sensors15
Engine Sensors

Engine Temperature Sensor

  • Monitors the operating temperature of the engine.
  • Exposed to engine coolant.
  • Engine cold = Low Resistance = Rich Mixture
  • Engine Hot = High Resistance = Lean Mixture.
engine sensors16
Engine Sensors

Mass Air Flow Sensor (MAF)

  • Measures the amount of outside air entering the engine.
  • Contains an air flap or door that operates a variable resistor.
  • Helps computer to determine how much fuel is needed.
engine sensors17
Engine Sensors

Inlet Air Temperature Sensor

  • Measures the temperature of air entering the engine.
  • Cold air (more dense) = More fuel for proper AF ratio.
engine sensors18
Engine Sensors

Crankshaft Position Sensor

  • Detects engine speed.
  • Changes injector timing and duration.
  • Higher engine speed = More fuel
engine idle speed control
Engine Idle Speed Control

Fast Idle Thermo Valve

  • Thermo wax plunger expands
  • and shrinks as the engine
  • warms up or cools down.
  • The thermo valve opens when cold to allow air to by-pass
  • the throttle valve.
  • This extra air increases engine idle speed to prevent cold engine
  • stalling.
engine idle speed control21
Engine Idle Speed Control

Idle Air Control Motor (IAC)

  • Computer opens the valve when temperature sensor signals
  • a cold engine.
  • Open = More Air = Increased Idle Speed.
throttle body injection
Throttle Body Injection
  • Uses one or two injectors.
  • Injectors (pulse) spray fuel into the
  • top of throttle body air horn.
  • Atomized fuel mixes with air and
  • drawn into the engine.
  • Fuel pressure regulator is spring loaded
  • and is part of the housing.
  • Fuel is being injected whenever the engine is running, also called CIS: Continuous Injection System.

EFI Multi port Injection System

  • Injector is pressed into the runner(Port)
  • in the intake manifold.
  • Injector sprays towards an engine
  • intake valve.
  • Each cylinder has it’s own injector

EFI Direct fuel Injection System

  • Injectors are pressed into the
  • combustion chamber and spray fuel
  • directly into the combustion chamber.
fuel injection diagnosis
Fuel Injection Diagnosis

***Do not be confused with ignition or engine mechanical problems.

  • Fuel leaks.
  • Vacuum leaks.
  • Kinked lines.
  • Sensor problems.
  • Loose or corroded electrical connections.

***Do not disconnect EFI harness terminal when ignition in

“on” position.


OBD (On Board Diagnostics) & OBD II

  • Most EFI systems have on-board diagnostic abilities.
  • ECM can detect and record possible faults.
  • MIL (Malfunction Indicator Light) in the dash-board glows when
  • any abnormality is sensed.
  • Scan tool will find and display many problems.
  • Always scan for trouble codes before attempting other diagnostic
  • procedures or disconnecting the battery (will clear codes).

Pressure Regulator Testing

***Caution – Relieve fuel pressure (up to 60psi)before disconnecting line.

  • Bleed Relief Valve or Fuse
  • Check fuel pressure with fuel pressure gauge
  • and match readings against the specs.
  • Fuel Pressure Too Low

Check clogged fuel filter or bad electric pump.

  • Fuel Pressure Too High

Usually bad pressure regulator.

Maximum Fuel Pressure Test

  • Pinch the return line with engine running (line with smaller diameter)
  • Check the gauge, if pressure too low, Fuel Pump, not the pressure
  • regulator is at fault.

Injector Testing

Bad injector can cause

  • Rough Idle
  • Hard Starting
  • Poor Fuel Economy
  • Engine Miss

Leaky Injectors will richen the

fuel mixture.

  • FAIR  -  but weak
  • 2. BAD  -  split spray pattern
  • 3. BAD  -  split spray pattern
  • BAD  -  jetting on left side
  • GOOD
  • 6. BAD  -  feathering at top of spray

Dirty Injectors restricts the air-

flow, causing a lean mixture.

Inoperative EFI Injectors

no action (Miss Fire)

tbi diagnosis
TBI Diagnosis
  • Check Pressure.
  • Fuel spray pattern can be seen into the horn.
  • If current and fuel pressure present, injector may be bad.
  • Regulator can be taken apart (GM).
  • Broke spring or bad diaphragm.
multi port diagnosis
Multi port Diagnosis
  • Listen for “clicking” sound at each injector with
  • a stethoscope.
  • Locate the bad injector.
  • Using an ohm meter check for resistance
  • across coil and short to ground.

Infinite Resistance=Open coil

Zero resistance to ground = shorted.


Injector noid light

  • Special test lights to check EFI feed circuit.
  • Injector cleaning kit can clean partially clogged injectors.

***caution – Some manufacturers do not recommend cleaning injectors

(Pintel Type)

oxygen sensor diagnosis
Oxygen Sensor Diagnosis
  • O2 voltage cycles from about 0.2 – 0.8 Volts.
  • 0.2 volts = lean AFR
  • 0.8 volts = Rich AFR
  • Simulate LEAN condition by pulling off a large vacuum hose.
  • (0.2 – 0.3 volts)
  • Simulate RICH condition by injecting propane into the air intake.
  • (0.7 – 0.8 volts)
temperature sensors
Temperature Sensors
  • Resistance can be checked by dipping it in hot Vs cold water.

Cold = Low resistance.

Hot = High resistance.