ORVR
DESCRIPTION
The ORVR (On-Board Refueling Vapor Recovery) system consists of a unique fuel tank, flow management valve,
fluid control valve, one-way check valve and vapor canister.
OPERATION
The ORVR (On-Board Refueling Vapor Recovery) system is used to remove excess fuel tank vapors. This is done
while the vehicle is being refueled.
Fuel flowing into the fuel filler tube (approx. 1” I.D.) creates an aspiration effect drawing air into the fuel fill tube.
During refueling, the fuel tank is vented to the EVAP 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
EVAP canister, the vehicle’s computer controlled purge system draws vapor out of the canister for the engine to
burn. The vapor 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 fuel 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 and on to thevapor canister. Vapor is absorbed in
the EVAP canister until vapor flow in the lines stops. This stoppage occursfollowing fuel shut-off, or by having the
fuel level in the tank rise high enough to close the control valve. This control valve contains a float that rises to seal
the large diameter vent path to the EVAP canister. At this point in the refueling process, fuel tank pressure
increases, the check valve closes (preventing liquid fuel from spiting back at the operator), and fuel then rises up
the fuel filler tube to shut off the dispensing nozzle.
PUMP-NATURAL VAC LEAK DETECTION
DESCRIPTION
Vehicles equipped with an NGC Powertrain Control Module (PCM) use a Natural Vacuum Leak Detection (NVLD)
pump and system. Vehicles equipped with a JTEC PCM use an LDP (Leak Detection Pump). Refer to Leak Detec-
tion Pump (LDP) for additional information.
The NVLD pump is located in the same area as the leak detection pump. Refer toNVLD Removal / Installation for
additional information.
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). 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
(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
Gas Law. 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 pres-
sure. 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 evaporativesystem 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 systemexceeds about 1
H2O (0.25 KPA), a
vacuum switch closes. The switch closure sends a signal to the NGC. The NGC,via appropriate logic strategies,
utilizes the switch signal, or lack thereof, to make a determination of whether a leak is present.
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 can-
ister. The NVLD assembly may be mounted on top of the canister outlet, or in-line between the canister and atmo-
spheric vent filter. The normally open vacuum switch will close with about1
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 fromfailednozzleliquidingestion,inorderto
detect cap off conditions.
The normally closed valve in the NVLD is intended to maintain the seal on theevaporative system during the engine
off condition. If vacuum in the evaporative system exceeds 3
to 6H2O (0.75 to 1.5 KPA), the valve will be pulled
off the seat, opening the seal. This will protect the system from excessivevacuum 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 an initial
1.5 amps of current to pull the valveopen, but after 100 mili-seconds, willbedutycycleddowntoanaverageof
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
blow offat about 0.5H2O (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
breatheduring increasing temperatures, thus
limiting the pressure in the tank to this low level. This is beneficial because the induced vacuum during a subse-
quent 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. Italso 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.
