DodgeForum.com - intrepid 2002 2.7l

This taken from manual
NATURAL VAC LEAK
DETECTION ASSY
DESCRIPTION

The natural Vacuum Leak detection (NVLD) system

is mounted on top of the EVAP canister (Fig. 3)

that is mounted on the fuel tank.

OPERATION

The Natural Vacuum Leak Detection (NVLD) system

is the next generation evaporative leak detection

system that will first be used on vehicles equipped

with the Next Generation Controller (NGC) starting

in 2002 M.Y. This new system replaces the leak

detection pump as the method of evaporative system

leak detection. This is to detect a leak equivalent to a

0.020

9 (0.5 mm) hole. This system has the capability

to detect holes of this size very dependably.

The basic leak detection theory employed with

NVLD is the

[font="times new roman"]39[font="times new roman"]40Gas Law4344. This is to say that the pressure

in a sealed vessel will change if the temperature

of the gas in the vessel changes. The vessel will only

see this effect if it is indeed sealed. Even small leaks

will allow the pressure in the vessel to come to equilibrium

with the ambient pressure. In addition to the

detection of very small leaks, this system has the

capability of detecting medium as well as large evaporative

system leaks.

A vent valve seals the canister vent during engine

off conditions. If the vapor system has a leak of less

than the failure threshold, the evaporative system

will be pulled into a vacuum, either due to the cool

down from operating temperature or diurnal ambient

temperature cycling. The diurnal effect is considered

one of the primary contributors to the leak determination

by this diagnostic. When the vacuum in the

system exceeds about 1

9 H2O (0.25 KPA), a vacuum

switch closes. The switch closure sends a signal to

the NGC. The NGC, via appropriate logic strategies

(described below), utilizes the switch signal, or lack

thereof, to make a determination of whether a leak is

present.

Fig. 2 UPSTREAM HEATED OXYGEN SENSOR 1/1

1 -

PROPORTIONAL PURGE SOLENOID

2 -

O2 SENSOR

Fig. 3 NVLD ASSEMBLY
LH
EVAPORATIVE EMISSIONS 25 - 13
EVAP/PURGE SOLENOID (Continued)

The NVLD device is designed with a normally open

vacuum switch, a normally closed solenoid, and a

seal, which is actuated by both the solenoid and a

diaphragm. The NVLD is located on the atmospheric

vent side of the canister. The NVLD assembly may

be mounted on top of the canister outlet, or in-line

between the canister and atmospheric vent filter. The

normally open vacuum switch will close with about 1

137[font="times new roman"]138

H2O (0.25 KPA) vacuum in the evaporative system.

The diaphragm actuates the switch. This is above the

opening point of the fuel inlet check valve in the fill

tube so cap off leaks can be detected. Submerged fill

systems must have recirculation lines that do not

have the in-line normally closed check valve that protects

the system from failed nozzle liquid ingestion,

in order to detect cap off conditions.

The normally closed valve in the NVLD is intended

to maintain the seal on the evaporative system during

the engine off condition. If vacuum in the evaporative

system exceeds 3

9 to 69 H2O (0.75 to 1.5 KPA),

the valve will be pulled off the seat, opening the seal.

This will protect the system from excessive vacuum

as well as allowing sufficient purge flow in the event

that the solenoid was to become inoperative.

The solenoid actuates the valve to unseal the canister

vent while the engine is running. It also will be

used to close the vent during the medium and large

leak tests and during the purge flow check. This solenoid

requires initial 1.5 amps of current to pull the

valve open but after 100 ms. will be duty cycled down

to an average of about 150 mA for the remainder of

the drive cycle.

Another feature in the device is a diaphragm that

will open the seal in the NVLD with pressure in the

evaporative system. The device will

[font="times new roman"]209210blow off9 at

about 0.5

9 H2O (0.12 KPA) pressure to permit the

venting of vapors during refueling. An added benefit

to this is that it will also allow the tank to

[font="times new roman"]233234breathe9

during increasing temperatures, thus limiting the

pressure in the tank to this low level. This is beneficial

because the induced vacuum during a subsequent

declining temperature will achieve the switch

closed (pass threshold) sooner than if the tank had to

decay from a built up pressure.

The device itself has 3 wires: Switch sense, solenoid

driver and ground. It also includes a resistor to

protect the switch from a short to battery or a short

to ground. The NGC utilizes a high-side driver to

energize and duty-cycle the solenoid.

REMOVAL

(1) Disconnect the negative battery cable.

(2) Remove fuel tank, refer to the Fuel Delivery

section for Fuel Tank Removal.

(3) Disconnect the electrical connector from the

NVLD assembly.

(4) Disconnect the hoses from the NVLD assembly

(Fig. 5).

(5) Lift tab on NVLD assembly (Fig. 4) and twist

the assembly counterclockwise and pull up to remove

from EVAP canister (Fig. 5).

(6) Remove O-ring from EVAP canister (Fig. 6).

INSTALLATION

(1) Install O-ring to EVAP canister (Fig. 6).

(2) Install NVLD assembly (Fig. 4) and twist the

assembly clockwise to lock assembly in the EVAP

canister (Fig. 5).

(3) Connect the hoses to the NVLD assembly.

(4) Connect the electrical connector to the NVLD

assembly.

Fig. 4 LOCKING TAB
Fig. 5 ASSEMBLY REMOVED
25 - 14 EVAPORATIVE EMISSIONS
LH
NATURAL VAC LEAK DETECTION ASSY (Continued)

(5) Install fuel tank, refer to the Fuel Delivery section

for Fuel Tank Installation.

(6) Connect the negative battery cable.

ORVR
DESCRIPTION

Onboard Refueling Vapor Recovery (ORVR) System

Schematic and components.

OPERATION

The emission control principle used in the ORVR

system is that the fuel flowing into the filler tube

(approx. 1” I.D.) creates an aspiration effect which

draws air into the fill tube (Fig. 7). During refueling,

the fuel tank is vented to the vapor canister to capture

escaping vapors. With air flowing into the filler

tube, there are no fuel vapors escaping to the atmosphere.

Once the refueling vapors are captured by

the canister, the vehicle’s computer controlled purge

system draws vapor out of the canister for the engine

to burn. The vapors flow is metered by the purge

solenoid so that there is no or minimal impact on

driveability or tailpipe emissions.

As fuel starts to flow through the fill tube, it opens

the normally closed check valve and enters the fuel

tank. Vapor or air is expelled from the tank through

the control valve to the vapor canister. Vapor is

absorbed in the canister until vapor flow in the lines

stops, either following shut-off or by having the fuel

level in the tank rise high enough to close the control

valve. The control valve contains a float that rises to

seal the large diameter vent path to the canister. At

this point in the fueling of the vehicle, the tank pressure

increase, the check valve closes (preventing tank

fuel from spiting back at the operator), and fuel then

rises up the filler tube to shut-off the dispensing nozzle.

If the engine is shut-off while the On-Board diagnostics

test is running, low level tank pressure can

be trapped in the fuel tank and fuel can not be added

to the tank until the pressure is relieved. This is due

to the leak detection pump closing the vapor outlet

from the top of the tank and the one-way check valve

not allowing the tank to vent through the fill tube to

atmosphere. Therefore, when fuel is added, it will

back-up in the fill tube and shut off the dispensing

nozzle. The pressure can be eliminated in two ways:

1. Vehicle purge must be activated and for a long

enough period to eliminate the pressure. 2. Removing

the fuel cap and allowing enough time for the system

to vent thru the recirulation tube.