Transcript Electronic Fuel Injection

Electronic Fuel Injection
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• Electronic Fuel Injection System Video
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Electronic Fuel Injection
• during the late 1970’s and early 1980’s, government imposed
minimum fuel mileage standards and tougher pollution control
standards meant the end of the carburetor
• Electronic Fuel Injection (EFI), was developed to help
manufacturers build vehicles that use less fuel, run cleaner and
perform better
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What is EFI?
• EFI uses a computer called a Powertrain Control Module (PCM) to
decide how much fuel the engine needs
• the computer turns on a fuel injector which sprays fuel, under
pressure, into the intake manifold or directly into the cylinder
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3 main types of fuel injection…
1) Throttle body injection (TBI)
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uses 1 or 2 injectors mounted on top of the throttle (fig. a)
performs better than a carburetor
unequal fuel distribution with some condensation
looks similar to a carburetor (fig. b)
low manufacturing costs
not as common today (used a lot in the 1980s)
fig. a
fig. b
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3 main types of fuel injection…
2) Multi-port or multi-point injection (MPFI)
• uses 1 injector for each cylinder
• much more common than TBI
• delivers the fuel more precisely than TBI
• more complex and costly compared to TBI
• intake manifold only delivers air so it can be designed for max. air flow
• improves low speed torque
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3 main types of fuel injection…
• 3) Direct injection (newest design) injects the fuel directly
into the combustion chamber
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How EFI Works
Input
Engine sensors
Processing
Computer
Output
Fuel quantity
Idle speed
Spark timing
Emission controls
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Input Section
• these sensors provide engine information to the PCM…
 engine speed sensor
 throttle position sensor
 coolant temperature sensor
 air temperature sensor
 engine load sensor
 knock (detonation) sensor
 oxygen sensor
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Input Section – Engine Speed
• engine speed, measured in RPM’s, is provided to
the PCM by either…
 the distributor’s pick-up coil (vehicles with
distributors) or…
 crankshaft position sensor (used on
distributorless & direct ignition)
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Input Section – Throttle Position
• throttle position sensor (TPS) tells the PCM how much pressure
the driver is putting on the throttle
• TPS is a variable resistor
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Input Section – TPS
• a 5 volt signal is sent to the TPS. A return signal is sent back
to the PCM that corresponds with throttle position.
• idle: ≈ .5 volt
• ½ throttle: ≈ 2.5 volts
• wide open throttle ≈4.5 volts
• PCM interprets these return voltages as specific throttle
positions.
• PCM can then adjust the quantity of fuel needed accordingly.
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TPS & PCM Wiring
• throttle position determines what portion of the 5 volt signal is at
the PCM’s signal terminal
PCM
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Input Section – Engine Temperature
• a coolant temperature sensor (CTS) is used to provide the
PCM with the temperature of the coolant
• the PCM can then inject more fuel the colder the engine is or
less fuel as the engine warms up
• the CTS is a temperature sensitive resistor (thermistor). As
the temperature increases, its resistance decreases
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Input Section – Air Temperature
• an air temperature sensor is used to provide the PCM with the
temperature of the air entering the intake manifold
• the PCM can then inject more fuel the colder the engine is or less
fuel as the engine warms up
• the air temperature sensor is a temperature sensitive resistor
 as the temperature increases, its resistance decreases
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Input Section – Engine Load
• a manifold absolute pressure sensor (MAP sensor) senses
engine vacuum and uses this signal as an indicator of the engine
load
• light engine load = higher vacuum = lower manifold pressure
• heavy engine load = lower vacuum = higher manifold pressure
• PCM responds by injecting more fuel into the engine during
heavy loads, or less fuel at light loads
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Input Section – Engine Load
• another way to measure engine
load is to measure how much air is
flowing into the engine
• mass airflow sensor (MAF) “tells”
the computer how much load is being
placed on the engine
• MAF measures airflow into the
engine in grams/second
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Input Section – Engine Load
• air flow can also be measured with an air flow meter
• uses a moveable flap
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Input Section – Spark Knock
• knock sensor can detect detonation & PCM will respond by
retarding the ignition timing
 detonation is combustion of the fuel that wasn’t initiated by
the spark plug
 this can be caused by excessive heat, carbon build-up or
low octane fuel
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Input Section – Oxygen Sensor
• the key to EFI’s ability to provide excellent fuel economy & low
emissions is the oxygen sensor (O2 sensor)
• the O2 sensor “tells” the PCM if the air-fuel mixture is too rich or
too lean. PCM then adjusts the AFM to keep it at the ideal ratio of
14.7:1
Tech Tip:
too rich means too much fuel
too lean means too little fuel
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How does the O2 sensor do that?
• the O2 sensor screws into the exhaust pipe
• as the exhaust gases leave the engine, the O2 sensor compares oxygen in the atmosphere to
oxygen left in the exhaust gases
• if there is little oxygen left over, this means the mixture is too rich
• if there is lots of oxygen left over, then the mixture is too lean
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O2 Sensor
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O2 Sensor Communication with the PCM
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if the mixture is too rich = little oxygen is left over in the exhaust gases
 O2 sensor produces ≈ 1 volt
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if the mixture is too lean = lots of oxygen left over in the exhaust gases
 O2 sensor produces a low voltage ≈ .1 volt
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if the mixture is perfect (14.7:1), then the O2 sensor will produce .5 volt
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Output Section
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Output Section – Fuel Delivery
• once the PCM has received all the data from the input sensors, it
then decides how much fuel to give the engine by varying how long
the injector is turned on
• injector on-time is called pulse width
 (measured in milliseconds)
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Output Section – Idle Speed Control
• the PCM is also responsible for controlling the idle speed
of the engine with an idle speed motor
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PCM Output Control
• in addition to fuel quantity & idle speed control, the PCM also
controls emission control devices
idle speed motor
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Fuel Delivery System
• most fuel injection systems operate at ≈35psi of fuel pressure
• electric fuel pump and fuel pressure regulator work together to maintain
30 – 60 psi
 TBI injection operates at lower pressures
 some multiport pressures are higher than 35psi
 direct injection can be in the 400 – 1500psi range
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Returnless Fuel Supply System
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used since the mid 90’s
uses an in-tank fuel pump & pressure regulator module
reduces fuel evaporative losses
PCM can vary fuel supply by modifying fuel pump pulse width
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Direct Injection Fuel Supply
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direct injection engines use an engine driven, high pressure
mechanical fuel pump…
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35PSI, as is found on port injection is insufficient for direct injection
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direct injection pressures must overcome compression pressures
37 sec.
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Gasoline Fuel Injection
• optimal way of delivering fuel to a spark ignition engine when
compared to carburetors
 more exact control of fuel delivery
 AFM ratio better matched to the engine working conditions
 better fuel economy
 fewer emissions
 less cylinder wear (less chance of fuel washing oil off cylinder)
 better performance (driveability)
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Electronic Throttle Control - AKA Drive-by-wire
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throttle cable is eliminated
PCM controls air flow into engine – not the driver
TPS is still used
Pedal Position Sensor (PPS) added
DC servo motor opens/closes throttle plate
PPS
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