Dodge Durango (DN). Manual — part 210

sion of fuel tank vapors into the atmosphere. When
fuel evaporates in the fuel tank, the vapors pass
through vent hoses or tubes to a charcoal filled evap-
orative canister. The canister temporarily holds the
vapors. The Powertrain Control Module (PCM) allows
intake manifold vacuum to draw vapors into the com-
bustion chambers during certain operating condi-
tions.

All engines use a duty cycle purge system. The

PCM controls vapor flow by operating the duty cycle
EVAP purge solenoid. Refer to Duty Cycle EVAP
Canister Purge Solenoid.

When equipped with certain emissions packages, a

Leak Detection Pump (LDP) will be used as part of
the evaporative system for OBD II requirements.
Also refer to Leak Detection Pump.

NOTE: The evaporative system uses specially man-
ufactured lines/hoses. If replacement becomes nec-
essary, only use fuel resistant hose.

ROLLOVER VALVE

DESCRIPTION

The fuel tank is equipped with two rollover valves.

The front valve is located on the top of the fuel pump

module (Fig. 1). The other valve is located on the top
rear of the fuel tank (Fig. 1).

OPERATION

The rollover valves will prevent fuel flow through

the fuel tank vent (EVAP) hoses in the event of an
accidental vehicle rollover. The EVAP canister draws
fuel vapors from the fuel tank through these valves.

The rear valve cannot be serviced separately. If

replacement is necessary, the fuel tank must be
replaced. Refer to Fuel Tank Removal/Installation in

Fig. 1 Rollover Valve Locations

1 – FUEL PUMP MODULE
2 – FRONT ROLLOVER VALVE
3 – FUEL FILTER/FUEL PRESSURE REGULATOR
4 – FUEL TANK
5 – EVAP LINE
6 – REAR ROLLOVER VALVE

25 - 24

EMISSION CONTROL SYSTEMS

Group 14, Fuel System. The front valve can be ser-
viced separately.

EVAPORATION (EVAP) CANISTER

DESCRIPTION

A maintenance free, EVAP canister is used on all

vehicles. The EVAP canister is located under the
vehicle, inside the left frame rail, in front of the fuel
tank (Fig. 2).

OPERATION

The EVAP canister is filled with granules of an

activated carbon mixture. Fuel vapors entering the
EVAP canister are absorbed by the charcoal granules.

Fuel tank pressure vents into the EVAP canister.

Fuel vapors are temporarily held in the canister until
they can be drawn into the intake manifold. The duty
cycle EVAP canister purge solenoid allows the EVAP
canister to be purged at predetermined times and at
certain engine operating conditions.

DUTY CYCLE EVAP CANISTER PURGE
SOLENOID

OPERATION

The duty cycle EVAP canister purge solenoid (DCP)

regulates the rate of vapor flow from the EVAP can-
ister to the intake manifold. The Powertrain Control
Module (PCM) operates the solenoid.

During the cold start warm-up period and the hot

start time delay, the PCM does not energize the sole-
noid. When de-energized, no vapors are purged. The
PCM de-energizes the solenoid during open loop oper-
ation.

The engine enters closed loop operation after it

reaches a specified temperature and the time delay
ends. During closed loop operation, the PCM cycles
(energizes and de-energizes) the solenoid 5 or 10
times per second, depending upon operating condi-
tions. The PCM varies the vapor flow rate by chang-
ing solenoid pulse width. Pulse width is the amount
of time that the solenoid is energized. The PCM
adjusts solenoid pulse width based on engine operat-
ing condition.

LEAK DETECTION PUMP (LDP)

OPERATION

The Leak Detection Pump (LDP) is used only with

certain emission packages.

The LDP is a device used to detect a leak in the

evaporative system.

The pump contains a 3 port solenoid, a pump that

contains a switch, a spring loaded canister vent valve
seal, 2 check valves and a spring/diaphragm.

Immediately after a cold start, engine temperature

between 40°F and 86°F, the 3 port solenoid is briefly
energized. This initializes the pump by drawing air
into the pump cavity and also closes the vent seal.
During non-test test conditions, the vent seal is held
open by the pump diaphragm assembly which pushes
it open at the full travel position. The vent seal will
remain closed while the pump is cycling. This is due
to the operation of the 3 port solenoid which prevents
the diaphragm assembly from reaching full travel.
After the brief initialization period, the solenoid is
de-energized, allowing atmospheric pressure to enter
the pump cavity. This permits the spring to drive the
diaphragm which forces air out of the pump cavity
and into the vent system. When the solenoid is ener-
gized and de-energized, the cycle is repeated creating
flow in typical diaphragm pump fashion. The pump
is controlled in 2 modes:

PUMP MODE: The pump is cycled at a fixed rate

to achieve a rapid pressure build in order to shorten
the overall test time.

TEST MODE: The solenoid is energized with a

fixed duration pulse. Subsequent fixed pulses occur
when the diaphragm reaches the switch closure
point.

The spring in the pump is set so that the system

will achieve an equalized pressure of about 7.5 inches
of water.

When the pump starts, the cycle rate is quite high.

As the system becomes pressurized pump rate drops.

Fig. 2 EVAP Canister Location

1 – LEFT FRAME RAIL
2 – RUBBER GROMMETS (2)
3 – LOCATING PINS (2)
4 – EVAP CANISTER
5 – MOUNTING NUT
6 – MOUNTING BRACKET

EMISSION CONTROL SYSTEMS

25 - 25

DESCRIPTION AND OPERATION (Continued)

If there is no leak the pump will quit. If there is a
leak, the test is terminated at the end of the test
mode.

If there is no leak, the purge monitor is run. If the

cycle rate increases due to the flow through the
purge system, the test is passed and the diagnostic is
complete.

The canister vent valve will unseal the system

after completion of the test sequence as the pump
diaphragm assembly moves to the full travel position.

A typical system schematic is shown in (Fig. 3).

POSITIVE CRANKCASE VENTILATION (PCV)
SYSTEM

DESCRIPTION

All 3.9L V-6 and 5.2/5.9L V-8 are equipped with a

closed crankcase ventilation system and a positive
crankcase ventilation (PCV) valve.

This system consists of a PCV valve mounted on

the cylinder head (valve) cover with a hose extending
from the valve to the intake manifold. Another hose
connects the opposite cylinder head (valve) cover to
the air cleaner housing to provide a source of clean
air for the system. A separate crankcase breather/fil-
ter is not used.

OPERATION

The PCV system operates by engine intake mani-

fold vacuum (Fig. 5). Filtered air is routed into the
crankcase through the air cleaner hose. The metered
air, along with crankcase vapors, are drawn through
the PCV valve and into a passage in the intake man-
ifold. The PCV system manages crankcase pressure
and meters blow by gases to the intake system,
reducing engine sludge formation.

The PCV valve contains a spring loaded plunger.

This plunger meters the amount of crankcase vapors

Fig. 3 Evaporative System Monitor Schematic—Typical

1 – DUTY CYCLE PURGE SOLENOID (DCPS) DRIVER
2 – POWERTRAIN CONTROL MODULE (PCM)
3 – 3-PORT SOLENOID DRIVER
4 – REMOTE FILTER
5 – COMBINED CANISTER VENT VALVE & LEAK DETECTION

PUMP

6 – CANISTER

7 – TANK ROLLOVER VALVE & VAPOR FLOW CONTROL

ORIFICE

8 – INTAKE MANIFOLD
9 – THROTTLE BODY
10 – DCPS
11 – SWITCH SIGNAL INPUT TO THE PCM
12 – ENGINE VACUUM LINE

25 - 26

EMISSION CONTROL SYSTEMS

DESCRIPTION AND OPERATION (Continued)

routed into the combustion chamber based on intake
manifold vacuum.

When the engine is not operating or during an

engine pop-back, the spring forces the plunger back
against the seat. This will prevent vapors from flow-
ing through the valve.

During periods of high manifold vacuum, such as

idle or cruising speeds, vacuum is sufficient to com-
pletely compress spring. It will then pull the plunger

to the top of the valve (Fig. 7). In this position there
is minimal vapor flow through the valve.

During periods of moderate manifold vacuum, the

plunger is only pulled part way back from inlet. This
results in maximum vapor flow through the valve
(Fig. 8).

POSITIVE CRANKCASE VENTILATION (PCV)
SYSTEM—4.7L ENGINE

DESCRIPTION

The 4.7L V-8 engine is equipped with a closed

crankcase ventilation system and a Positive Crank-
case Ventilation (PCV) valve.

This system consists of:
• a PCV valve mounted to the oil filler housing

(Fig. 9). The PCV valve is sealed to the oil filler
housing with an o-ring.

• the air cleaner housing

• two interconnected breathers threaded into the

rear of each cylinder head (Fig. 10).

• tubes and hose to connect the system compo-

nents.

Fig. 4 PCV Valve/Hose—Typical

1 – PCV VALVE
2 – PCV VALVE HOSE CONNECTIONS

Fig. 5 Typical Closed Crankcase Ventilation System

1 – THROTTLE BODY
2 – AIR CLEANER
3 – AIR INTAKE
4 – PCV VALVE
5 – COMBUSTION CHAMBER
6 – BLOW-BY GASES
7 – CRANKCASE BREATHER/FILTER

Fig. 6 Engine Off or Engine Pop-Back—No Vapor

Flow

Fig. 7 High Intake Manifold Vacuum—Minimal Vapor

Flow

Fig. 8 Moderate Intake Manifold Vacuum—Maximum

Vapor Flow

EMISSION CONTROL SYSTEMS

25 - 27

DESCRIPTION AND OPERATION (Continued)

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Dodge Durango (DN). Manual — part 210

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