Emission Control - Subaru 2002 Impreza Service Manual

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SYSTEM OVERVIEW
Emission
Control
(Aux.
Emission Control
Devices)
Intake air tempera-
ture and pressure
sensor
ECM
Crankshaft position
sensor
Camshaft position
sensor
Engine coolant tern-
perature sensor
Knock sensor
1. System Overview
There are three emission control systems which are as follows:
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Crankcase emission control system
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Exhaust emission control system
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Three-way catalyst system
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Air/fuel (A/F) control system
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Ignition control system
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On-board refueling vapor recovery (ORVR) system
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Evaporative emission control system
Detects absolute pressure of intake manifold.
Detects intake air temperature of intake manifold.
Receives various signals, compares signals with basic data stored in
memory, and emits a signal for optimal control of ignition timing.
Detects engine speed (Revolution).
Detects reference signal for combustion cylinder discrimination.
Detects coolant temperature.
Detects engine knocking.
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Main components
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Function
;rankcase emission control
system
Exhaust
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Catalyst
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Front
mission
:ontrol
system
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A/F control
Positive crankcase
ventilation (PCV)
valve
Three-way catalyst
Engine control mod-
ule (ECM)
Draws blow-by gas into intake manifold from crankcase and burns it
together with air-fuel mixture. Amount of blow-by gas to be drawn in
is controlled by intake manifold pressure.
Oxidizes HC and CO contained in exhaust gases as well as reducing
NOx.
Receives input signals from various sensors, compares signals with
stored data, and emits a signal for optimal control of air-fuel mixture
ratio.
Front oxygen (NF)
sensor
Detects quantity of oxygen contained exhaust gases.
Rear oxygen sensor
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Detects density of oxygen contained exhaust gases.
Throttle position
sensor
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Detects throttle position.
Evaporative emission control
system
3RVR system
Canister Absorbs evaporative gas which occurs in fuel tank when engine
stops, and releases it to combustion chambers for a complete burn
when engine is started. This prevents HC from being discharged into
atmosphere.
Purge control
solenoid valve absorbed by canister.
Receives a signal from ECM and controls purge of evaporative gas
Pressure control
solenoid valve in fuel tank.
Receives a signal from ECM and controls evaporative gas pressure
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Ventvalve [Controls evaporation pressure in fuel tank.
Closes the evaporation line by receiving a signal from ECM to check
evaporation gas leak.
I-Drainvalve
EC-2