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
•Smoother idle
•Improved fuel economy
•Lower emissions
•Better cold weather drivability
•Increased engine power
•Simpler
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 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 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
•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 filter
•Throttle valve
•Sensors
•Connecting ducts
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
•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
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 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 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 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 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 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 Sensors
Inlet Air Temperature Sensor
•Measures the temperature of air entering the engine.
•Cold air (more dense) = More fuel for proper AF ratio.
Engine Sensors
Crankshaft Position Sensor
•Detects engine speed.
•Changes injector timing and duration.
•Higher engine speed = More fuel
Engine Sensors
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 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
•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
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
***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.
Diagnosis
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).
Diagnosis
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.
Diagnosis
Injector Testing
Bad injector can cause
•Rough Idle
•Hard Starting
•Poor Fuel Economy
•Engine Miss
Leaky Injectors will richen the
fuel mixture.
Dirty Injectors restricts the airflow, causing a lean mixture.
Inoperative EFI Injectors
no action (Miss Fire)
1. FAIR - but weak
2. BAD - split spray pattern
3. BAD - split spray pattern
4. BAD - jetting on left side
5. GOOD
6. BAD - feathering at top of spray
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
•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.
Diagnosis
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
•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
•Resistance can be checked by dipping it in hot Vs cold water.
Cold = Low resistance.
Hot = High resistance.