Dodge Ram Truck 1500-2500-3500. Manual — part 2085

SPECIFICATIONS

TORQUE - EVAP SYSTEM

DESCRIPTION

N·m

Ft. Lbs.

In. Lbs.

EVAP Canister Mounting

Nuts

11

-

95

EVAP Canister Mounting

Bracket-to-Frame Bolts

14

10

125

Leak Detection Pump

Mounting Bolts

11

-

95

Leak Detection Pump

Filter Mounting Bolt

11

-

95

SOLENOID - EVAP/PURGE

DESCRIPTION

The duty cycle EVAP canister purge solenoid is located in the engine compartment. It is attached to the side of the
Power Distribution Center (PDC).

OPERATION

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 solenoid. When
de-energized, no vapors are purged. The PCM de-energizes the solenoid during open loop operation.

The engine enters closed loop operation after it reaches a specified temperature and the time delay ends. During
closed loop operation, the PCM energizes and de-energizes the solenoid 5 or 10 times per second, depending upon
operating conditions. The PCM varies the vapor flow rate by changing solenoid pulse width. Pulse width is the
amount of time the solenoid energizes. The PCM adjusts solenoid pulse width based on engine operating condition.

REMOVAL

The duty cycle EVAP canister purge solenoid (3) is
located in the engine compartment. It is attached to
the side of the Power Distribution Center (PDC).

1. Disconnect electrical wiring connector at solenoid.

2. Disconnect vacuum harness (2) at solenoid.

3. Remove solenoid from mounting bracket.

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EVAPORATIVE EMISSIONS

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INSTALLATION

1. Install solenoid assembly to mounting bracket.

2. Connect vacuum harness.

3. Connect electrical connector.

CAP - FUEL FILLER

DESCRIPTION

The plastic fuel tank filler tube cap is threaded onto the end of the fuel fill tube. Certain models are equipped with
a 1/4 turn cap.

OPERATION

The loss of any fuel or vapor out of fuel filler tube is prevented by the use of a pressure-vacuum fuel fill cap. Relief
valves inside the cap will release fuel tank pressure at predetermined pressures. Fuel tank vacuum will also be
released at predetermined values. This cap must be replaced by a similar unit if replacement is necessary. This is
in order for the system to remain effective.

CAUTION: Remove fill cap before servicing any fuel system component to relieve tank pressure. If equipped
with a Leak Detection Pump (LDP), or NVLD system, the cap must be tightened securely. If cap is left loose,
a Diagnostic Trouble Code (DTC) may be set.

REMOVAL

REMOVAL/INSTALLATION

If replacement of the 1/4 turn fuel tank filler tube cap is necessary, it must be replaced with an identical cap to be
sure of correct system operation.

CAUTION: Remove the fuel tank filler tube cap to relieve fuel tank pressure. The cap must be removed prior
to disconnecting any fuel system component or before draining the fuel tank.

PUMP - LEAK DETECTION

DESCRIPTION

Vehicles equipped with JTEC engine control modules use a leak detection pump. Vehicles equipped with NGC
engine control modules use an NVLD pump. Refer to Natural Vacuum - Leak Detection (NVLD) for additional infor-
mation.

The evaporative emission system is designed to prevent the escape of fuel vapors from the fuel system. Leaks in
the system, even small ones, can allow fuel vapors to escape into the atmosphere. Government regulations require
onboard testing to make sure that the evaporative (EVAP) system is functioning properly. The leak detection system
tests for EVAP system leaks and blockage. It also performs self-diagnostics. During self-diagnostics, the Powertrain
Control Module (PCM) first checks the Leak Detection Pump (LDP) for electrical and mechanical faults. If the first
checks pass, the PCM then uses the LDP to seal the vent valve and pump air into the system to pressurize it. If a
leak is present, the PCM will continue pumping the LDP to replace the air that leaks out. The PCM determines the
size of the leak based on how fast/long it must pump the LDP as it tries to maintain pressure in the system.

DR/DH

EVAPORATIVE EMISSIONS

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EVAP LEAK DETECTION SYSTEM
COMPONENTS

Service Port: Used with special tools like the Miller
Evaporative Emissions Leak Detector (EELD) to test
for leaks in the system.

EVAP Purge Solenoid: The PCM uses the EVAP
purge solenoid to control purging of excess fuel
vapors stored in the EVAP canister. It remains closed
during leak testing to prevent loss of pressure.

EVAP Canister: The EVAP canister stores fuel vapors
from the fuel tank for purging.

EVAP Purge Orifice: Limits purge volume.

EVAP System Air Filter: Provides air to the LDP for
pressurizing the system. It filters out dirt while allowing
a vent to atmosphere for the EVAP system.

OPERATION

The main purpose of the LDP is to pressurize the fuel system for leak checking. It closes the EVAP system vent to
atmospheric pressure so the system can be pressurized for leak testing. The diaphragm is powered by engine vac-
uum. It pumps air into the EVAP system to develop a pressure of about 7.5

9

H2O (1/4) psi. A reed switch in the LDP

allows the PCM to monitor the position of the LDP diaphragm. The PCM uses the reed switch input to monitor how
fast the LDP is pumping air into the EVAP system. This allows detection of leaks and blockage. The LDP assembly
consists of several parts. The solenoid is controlled by the PCM, and it connects the upper pump cavity to either
engine vacuum or atmospheric pressure. A vent valve closes the EVAP system to atmosphere, sealing the system
during leak testing. The pump section of the LDP consists of a diaphragm that moves up and down to bring air in
through the air filter and inlet check valve, and pump it out through an outlet check valve into the EVAP system. The
diaphragm is pulled up by engine vacuum, and pushed down by spring pressure, as the LDP solenoid turns on and
off. The LDP also has a magnetic reed switch to signal diaphragm position to the PCM. When the diaphragm is
down, the switch is closed, which sends a 12 V (system voltage) signal to the PCM. When the diaphragm is up, the
switch is open, and there is no voltage sent to the PCM. This allows the PCM to monitor LDP pumping action as it
turns the LDP solenoid on and off.

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EVAPORATIVE EMISSIONS

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LDP AT REST (NOT POWERED)

When the LDP is at rest (no electrical/vacuum) the
diaphragm is allowed to drop down if the internal
(EVAP system) pressure is not greater than the return
spring. The LDP solenoid blocks the engine vacuum
port and opens the atmospheric pressure port con-
nected through the EVAP system air filter. The vent
valve is held open by the diaphragm. This allows the
canister to see atmospheric pressure.

DIAPHRAGM UPWARD MOVEMENT

When the PCM energizes the LDP solenoid, the sole-
noid blocks the atmospheric port leading through the
EVAP air filter and at the same time opens the engine
vacuum port to the pump cavity above the diaphragm.
The diaphragm moves upward when vacuum above
the diaphragm exceeds spring force. This upward
movement closes the vent valve. It also causes low
pressure below the diaphragm, unseating the inlet
check valve and allowing air in from the EVAP air fil-
ter. When the diaphragm completes its upward move-
ment, the LDP reed switch turns from closed to open.

DR/DH

EVAPORATIVE EMISSIONS

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