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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 System

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Fuel injection system l.jpg

Fuel Injection System

Fuel injection system2 l.jpg

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 l.jpg

Fuel Injection System


  • Improved Atomization

  • Better fuel flow

  • Smoother idle

  • Improved fuel economy

  • Lower emissions

  • Better cold weather drivability

  • Increased engine power

  • Simpler

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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.

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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.

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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

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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 l.jpg

Air Induction System

  • Air filter

  • Throttle valve

  • Sensors

  • Connecting ducts

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Engine Sensors

Inlet Air Temperature Sensor

  • Measures the temperature of air entering the engine.

  • Cold air (more dense) = More fuel for proper AF ratio.

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Engine Sensors

Crankshaft Position Sensor

  • Detects engine speed.

  • Changes injector timing and duration.

  • Higher engine speed = More fuel

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Engine Sensors

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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.

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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.

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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.

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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.

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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.

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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).

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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.

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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)

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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.

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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.

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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)

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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)

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Temperature Sensors

  • Resistance can be checked by dipping it in hot Vs cold water.

Cold = Low resistance.

Hot = High resistance.

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