Engine Control System & Engine Component Tests: Operation: ORVR
The emission control principle used in ORVR system is that fuel flowing into filler tube (approximately 1" I.D.) creates an aspiration effect which draws air into fill tube. See Fig 1 . During refueling, fuel tank is vented to vapor canister to capture escaping vapors. With air flowing into filler tube, there are no fuel vapors escaping to atmosphere. Once refueling vapors are captured by canister, vehicle's computer controlled purge system draws vapor out of canister for engine to burn. The vapors flow is metered by purge solenoid so that there is no or minimal impact on driveability or tailpipe emissions.
As fuel starts to flow through fill tube, it opens normally closed check valve and enters fuel tank. Vapor or air is expelled from tank through control valve to vapor canister. Vapor is absorbed in canister until vapor flow in lines stops, either following shut-off or by having fuel level in tank rise high enough to close control valve. The control valve contains a float that rises to seal large diameter vent path to canister. At this point in fueling of vehicle, tank pressure increase, check valve closes (preventing tank fuel from spiting back at operator), and fuel then rises up filler tube to shut-off dispensing nozzle.
If engine is shut-off while On-Board diagnostics test is running, low level tank pressure can be trapped in fuel tank and fuel can not be added to tank until pressure is relieved. This is due to leak detection pump closing vapor outlet from top of tank and one-way check valve not allowing tank to vent through fill tube to atmosphere. Therefore, when fuel is added, it will back-up in fill tube and shut off dispensing nozzle. The pressure can be eliminated in 2 ways:
- Vehicle purge must be activated and for a long enough period to eliminate pressure.
- Removing fuel cap and allowing enough time for system to vent through recirculation tube.