Service Manuals, User Guides, Schematic Diagrams or docs for : . Car Manuals Subaru Impreza 2001-2002.2004-2007 Approved Subaru Impreza 2004 WRX STi 08. MECHANISM AND FUNCTION 13. EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES) 01. System Overview
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W1860BE.book Page 2 Tuesday, January 28, 2003 11:01 PM
SYSTEM OVERVIEW
EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES)
1. System Overview
There are three emission control systems which are as follows:
Crankcase emission control system
Exhaust emission control system
Three-way catalytic converter
Air/fuel (A/F) control system
Ignition control system
Evaporative emission control system
EC(H4DOTC)-2
W1860BE.book Page 3 Tuesday, January 28, 2003 11:01 PM
SYSTEM OVERVIEW
EMISSION CONTROL (AUX. EMISSION CONTROL DEVICES)
Item Main components Function
Crankcase emission control Positive crankcase ventilation Draws blow-by gas into intake manifold from crankcase and
system (PCV) valve burns it together with air-fuel mixture. Amount of blow-by gas to
be drawn in is controlled by intake manifold pressure.
Exhaust Catalyt- Pre Catalytic converter Oxidizes HC and CO contained in exhaust gases as well as re-
emis- ic con- ducing NOx.
Front
sion verter
control Rear
system
Air/fuel (A/F) con- Engine control module (ECM) Receives input signals from various sensors, compares signals
trol system with stored data, and emits a signal for optimal control of air-fuel
mixture ratio.
Front oxygen (A/F) sensor Detects density of oxygen contained exhaust gases.
Rear oxygen sensor Detects density of oxygen contained in exhaust gases.
Throttle position sensor Detects throttle opening.
Manifold absolute pressure Detects absolute pressure of intake manifold.
sensor
Mass air flow and intake air Detects amount of intake air.
temperature sensor
Detects intake air temperature at air cleaner case.
Ignition control sys- ECM Receives various signals, compares signals with basic data
tem stored in memory, and emits a signal for optimal control of igni-
tion timing.
Crankshaft position sensor Detects engine speed (revolution).
Camshaft position sensor Detects reference signal for combustion cylinder discrimination.
Engine coolant temperature Detects coolant temperature.
sensor
Knock sensor Detects engine knocking.
Evaporative emission control Canister Absorbs evaporative gas which occurs in fuel tank when engine
system stops, and releases it to combustion chambers for a complete
burn when engine is started. This prevents HC from being dis-
charged into atmosphere.
Purge control solenoid valve Receives a signal from ECM and controls purge of evaporative
gas absorbed by canister.
Pressure control solenoid Receives a signal from ECM and controls evaporative gas pres-
valve sure in fuel tank.
ORVR system Vent valve Controls evaporation pressure in fuel tank.
Drain valve Closes the evaporation line by receiving a signal from ECM to
check the evaporation gas leak.
EC(H4DOTC)-3
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