EVAPORATIVE EMISSION CONTROLS
TABLE OF CONTENTS
page page
DESCRIPTION AND OPERATION
EVAPORATION CONTROL SYSTEM ..........20
EVAP CANISTER .........................20
PROPORTIONAL PURGE SOLENOID—PCM
OUTPUT ..............................20
LEAK DETECTION PUMP ..................21
LEAK DETECTION PUMP PRESSURE
SWITCH ..............................22
POSITIVE CRANKCASE VENTILATION (PCV)
SYSTEMS.............................23
POSITIVE CRANKCASE VENTILATION VALVE. . . 23
VEHICLE EMISSION CONTROL
INFORMATION LABEL ...................24
DIAGNOSIS AND TESTING
PCV SYSTEM INSPECTION.................24
LEAK DETECTION PUMP ..................25
REMOVAL AND INSTALLATION
EVAP CANISTER .........................25
LEAK DETECTION PUMP ..................26
PROPORTIONAL PURGE SOLENOID VALVE....26
DESCRIPTION AND OPERATION
EVAPORATION CONTROL SYSTEM
OPERATION
The evaporation control system prevents the emis-
sion of fuel tank vapors into the atmosphere. When
fuel evaporates in the fuel tank, the vapors pass
through vent hoses or tubes to an activated carbon
filled evaporative canister. The canister temporarily
holds the vapors. The Powertrain Control Module
(PCM) allows intake manifold vacuum to draw
vapors into the combustion chambers during certain
operating conditions (Fig. 1).
All engines use a proportional purge solenoid sys-
tem. The PCM controls vapor flow by operating the
purge solenoid. Refer to Proportional Purge Solenoid
in this section.
NOTE: The evaporative system uses specially man-
ufactured hoses. If they need replacement, only use
fuel resistant hose. Also the hoses must be able to
pass an Ozone compliance test.
NOTE: For more information on Onboard Refueling
Vapor Recovery (ORVR), refer to the Fuel Delivery
section.
EVAP CANISTER
DESCRIPTION
The canister protrudes through the top of the
bracket. The vacuum and vapor tubes connect to the
top of the canister (Fig. 2). It is a charcoal canister.
OPERATION
All vehicles use a, maintenance free, evaporative
(EVAP) canister. Fuel tank vapors vent into the can-
ister. The canister temporarily holds the fuel vapors
until intake manifold vacuum draws them into the
combustion chamber. The Powertrain Control Module
(PCM) purges the canister through the proportional
purge solenoid. The PCM purges the canister at pre-
determined intervals and engine conditions.
PROPORTIONAL PURGE SOLENOID—PCM
OUTPUT
DESCRIPTION
All vehicles use a proportional purge solenoid. The
solenoid regulates the rate of vapor flow from the
EVAP canister to the throttle body. The PCM oper-
ates the solenoid.
25 - 20 EMISSION CONTROL SYSTEMS LH
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