ORVR
OPERATION
The emission control principle used in the ORVR
system is that the fuel flowing into the filler tube
(appx. 1º I.D.) creates an aspiration effect which
draws air into the fill tube (Fig. 9). During refueling,
the fuel tank is vented to the vapor canister to cap-
ture escaping vapors. With air flowing into the filler
tube, there are no fuel vapors escaping to the atmo-
sphere. 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(Refer to 14 - FUEL SYS-
TEM/FUEL DELIVERY/FUEL TANK - OPERATION)
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 increases, the check
valve closes (preventing tank fuel from spitting 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 diag-
nostics 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.
Fig. 7 LDP LOCATION
Fig. 8 LDP REMOVAL/INSTALLATION
25 - 14 EVAPORATIVE EMISSIONSRS
LEAK DETECTION PUMP (Continued)
