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EMISSION CONTROL SYSTEMS
25 - 1
EMISSION CONTROL SYSTEMS
CONTENTS
page
page
COMPONENT REMOVAL/INSTALLATION . . . . . . 8
EVAPORATIVE EMISSION CONTROLS . . . . . . . 4
EXHAUST EMISSION CONTROLS . . . . . . . . . . . 7
GENERAL INFORMATION . . . . . . . . . . . . . . . . . . 1
GENERAL INFORMATION
INDEX
page
DRB Scan Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Service Reminder Indicator (SRI) Lamp . . . . . . . . . 1
page
Vacuum Hose Routing Schematics . . . . . . . . . . . . 1
Vehicle Emission Control Information (VECI) Label . 1
SERVICE REMINDER INDICATOR (SRI) LAMP
The instrument panel mounted SRI lamp was for-
merly referred to as the emission maintenance re-
minder (EMR) lamp. It is
not used
on any Jeep
model for the 1994 model year.
VEHICLE EMISSION CONTROL INFORMATION
(VECI) LABEL
All vehicles are equipped with a combined VECI
label. The label is located in the engine compartment
(Figs. 1 or 2). The label contains the following:
•
Engine family and displacement
•
Evaporative family
•
Emission control system schematic
•
Certification application
•
Engine timing specifications (if adjustable)
•
Idle speeds (if adjustable)
•
Spark plug and plug gap
The label also contains an engine vacuum sche-
matic. There are unique labels for vehicles built for
sale in the state of California and the country of
Canada. Canadian labels are written in both the En-
glish and French languages. These labels are perma-
nently attached and cannot be removed without
defacing information and destroying it.
The VECI label illustration (Fig. 3) is used as
an example only.
Refer to the VECI label located in
the engine compartment (Figs. 1 or 2) for actual
emission information.
Fig. 1 VECI Label Location—XJ Models
VACUUM HOSE ROUTING SCHEMATICS
The vacuum hose routing schematics are used
as examples only.
If there are any differences be-
tween these schematics and the Vehicle Emission
Fig. 2 VECI Label Location—YJ Models
25 - 2
EMISSION CONTROL SYSTEMS
J
Fig. 3 VECI Label—Typical
Control Information (VECI) label schematics, those
shown on the VECI label should be used.
DRB SCAN TOOL
For operation of the DRB scan tool, refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual.
VACUUM ROUTING SCHEMATIC—2.5L 4 CYLINDER ENGINE
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EMISSION CONTROL SYSTEMS
VACUUM ROUTING SCHEMATIC—4.0L 6 CYLINDER ENGINE
25 - 3
25 - 4
EMISSION CONTROL SYSTEMS
EVAPORATIVE EMISSION CONTROLS
INDEX
page
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page
Fuel Tank Filler Tube Cap
.................. 4
Pressure Relief/Rollover Valve . . . . . . . . . . . . . . . . 5
Crankcase Ventilation System . . . . . . . . . . . . . . . . 5
EVAP (Evaporation) Control System . . . . . . . . . . . 4
EVAP Canister . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
EVAP (EVAPORATION) CONTROL SYSTEM
GENERAL INFORMATION
The function of the EVAP control system is to pre-
vent the emissions of gasoline vapors from the fuel
tank into the atmosphere. When fuel evaporates in
the fuel tank, the vapors pass through vent hoses or
tubes to a carbon filled EVAP canister. They are
temporarily held in the canister until they can be
drawn into the intake manifold when the engine is
running.
The EVAP canister is a feature on all models for
the storage of fuel vapors from the fuel tank.
The hoses used in this system are specially
manufactured. If replacement becomes neces-
sary, it is important to use only fuel resistant
hose.
Fig. 5 EVAP Canister Location—YJ Models
CANISTER OPERATION
The EVAP canister is equipped with a vacuum con-
trolled purge shutoff switch (orifice) (Figs. 4 or 5)
that controls canister purge operation. The switch is
open when manifold vacuum is applied to it. When
the engine is operating, the EVAP canister purge
function draws fresh air through the top of the can-
ister. This causes the stored vapors to be drawn out
of the canister and into the airstream in the air
cleaner snorkel (Fig. 6).
The air cleaner contains a venturi in the air
cleaner cover used as a purge line vacuum source
(Fig. 6). The venturi effect increases the speed of the
intake air flowing by the slots in the venturi wall.
This creates a low pressure area around the slots.
When the purge shutoff switch is open, vapors from
the canister are drawn through slots and into the
airstream flowing through the venturi (Fig. 7). The
vapors pass through the intake manifold into the en-
gine combustion chambers where they are consumed
during engine combustion.
EVAP CANISTER
A sealed, maintenance free, EVAP canister is used
on all vehicles. On XJ models, the EVAP canister is
located in the engine compartment on the passenger
side frame rail (Fig. 4). On YJ models, the EVAP
canister is located in the engine compartment on the
dash panel and below the brake master cylinder (Fig.
5). The EVAP canister is filled with granules of an
activated carbon mixture. Fuel vapors entering the
EVAP canister are absorbed by the charcoal gran-
ules.
FUEL TANK FILLER TUBE CAP
The fuel tank filler tube cap incorporates a two-
way relief valve that is closed to atmosphere during
normal operating conditions. The relief valve used in
fuel filler caps of all models is calibrated at a pres-
sure of 10 kPa (1.5 psi) or a vacuum of 6 kPa (1.8 in.
Hg). When the pressure or vacuum is relieved, the
valve returns to the normally closed position.
Fig. 4 EVAP Canister Location—XJ Models
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EMISSION CONTROL SYSTEMS
25 - 5
Fig. 8 CCV System—2.5L Engine—Typical
Fig. 6 EVAP System—Typical
Fig. 9 CCV System—4.0L Engine—Typical
fixed orifice of a calibrated size. It meters the
amount of crankcase vapors drawn out of the engine.
On 2.5L engines, a fitting on drivers side of cylin-
der head (valve) cover contains the metered orifice. It
is connected to manifold vacuum.
A fresh air supply hose from the air cleaner is con-
nected to front of cylinder head cover on 4.0L en-
gines. It is connected to rear of cover on 2.5L
engines.
When the engine is operating, fresh air enters the
engine and mixes with crankcase vapors. Manifold
vacuum draws the vapor/air mixture through the
fixed orifice and into the intake manifold. The vapors
are then consumed during combustion.
Fig. 7 Air Cleaner Venturi—Typical
CAUTION: The fuel filler cap must be removed prior
to disconnecting any fuel system component.
CRANKCASE VENTILATION SYSTEM
All 2.5L 4 cylinder and 4.0L 6 cylinder engines are
equipped with a Crankcase Ventilation (CCV) system
(Figs. 8 or 9). The CCV system performs the same
function as a conventional PCV system, but does not
use a vacuum controlled valve.
On 4.0L engines, a molded vacuum tube connects
manifold vacuum to top of cylinder head (valve)
cover at dash panel end. The vacuum tube contains a
PRESSURE RELIEF/ROLLOVER VALVE
All vehicles are equipped with a combination fuel
tank pressure relief and rollover valve (Fig. 10). This
dual function valve will relieve fuel tank pressure
and also prevent fuel flow through the fuel tank vent
hoses in the event of an accidental vehicle rollover.
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