Even though the EVAP system performed well, it could not control the hydrocarbons escaping during refueling. Starting in 1998, vehicles were required to have an On-board Re-fueling and Vapor Recovery (ORVR). The vapor return systems installed on gas pump nozzles had relatively little effect on the amount of vapor escaping.
As a result, the ORVR system was created to trap the hydrocarbons released during refueling. An ORVR system was designed to control vapors produced during refueling by routing them to the canister during fuel refill.
As fuel is channeled into the Fuel Tank, the ORVR system directs the fuel vapor to be stored in the EVAP Canister. This vapor is later routed to the engine to be burned during normal combustion. The EVAP and ORVR systems have been very successful in the containment of hydrocarbon emissions.
To see how this is accomplished, let’s first take a look at the components in the system: The ORVR system can consist of the following:
1. Fuel Filler Neck: The filler neck on many models consists of the main pipe for the fuel delivery into the tank, the one or smaller lines that help control fuel vapor flow, and tank overflow control. The ORVR fuel filler neck is designed to make a dynamic liquid seal, dispensing fuel from the fuel nozzle. The smaller diameter filler neck creates suction around the fill neck opening. It draws air and any escaping vapors into the filler neck to be pushed into the tank during refueling.
2. Fuel Shut-Off (Fuel Cut) Valve: The fuel cut valve (anti-spit back) valve prevents fuel from splashing back up the filler neck. The spring-loaded valve opens automatically when refueling. The force of the fuel flowing is enough to open the valve when refueling.
3. Fill Vent Valve: The fill vent valve controls the flow of vapors during refueling. The valve is open when the tank is near empty. As fuel enters the tank, the vapors flow into the charcoal canister through the fill vent valve. A float in the valve rises as the fuel level approaches the full point. When the tank is full, the valve is closed to prevent liquid fuel from going through the valve.
4. Fuel Rollover Valve: The primary purpose of the rollover valve is to allow vapors to flow from the fuel tank to the charcoal canister. When the vehicle is parked on a steep incline, the valve is closed to prevent fuel spillage from the fuel tank into the charcoal canister. In the event of a vehicle rollover, it keeps liquid fuel out of the EVAP canister.
5. Fuel Liquid/Vapor Separator: The liquid-vapor separator prevents liquid fuel droplets from reaching the vapor canister. A barrier inside the separator allows vapor to travel freely, but fuel droplets are too heavy and trapped. The droplets either travel back into the fuel tank or vaporize and are stored in the charcoal canister.
6. Two-Way Valve for Pressure/Vacuum Relief: The two-way valve is a directional valve that allows fresh air into the charcoal canister. The valve also acts as a pressure relief valve if the system pressure gets too high. The arrow on the valve points toward the charcoal canister. When testing this valve, air should pass easily in one direction, and airflow should be somewhat restricted in the other direction. When replacing this valve, refer to the system diagram for the correct installation. The arrow on the valve indicates the direction of airflow. This valve must be installed in the right direction.
7. Hoses, Pipes, and Gaskets: The hoses, pipes, and clamping devices are critical to proper ORVR operation. Misrouted, damaged, or disconnected hoses can cause various symptoms, including difficulty filling the fuel tank with fuel or the MIL light coming “ON” for an evaporative system leak Diagnostic Trouble Code (DTC).
8. Charcoal Canister: The charcoal canister stores fuel vapors. The canister contains activated charcoal. During refueling, the charcoal can absorb fuel vapors, cleaning the vapor mixture and allowing uncontaminated air to escape into the atmosphere. Fresh air drawn into the canister during purging releases the fuel vapors and recharges the charcoal. Details of this are covered in the evaporative system components section.
These components work together with the ECM to prevent fuel vapor from escaping and route it to the intake manifold to be burned during normal combustion. Either through heat or agitation, fuel vapor builds up inside the Fuel Tank.
The fill pipe diameter reduces after the unleaded restrictor plate. This restricted pipe size forms a liquid seal into the tank rather than letting fumes escape. The check valve is spring-loaded to prevent fuel from entering the filler pipe. During refueling, a small amount of air is drawn into the filler pipe to prevent fuel vapors from escaping into the air during refueling. These vapors are drawn into the fuel nozzle and returned to the station’s tank.
The vapor valve vents to the canister through the ORVR valve, which has a float to close off the vent when the tank is full. A faulty ORVR valve can leak or cause difficulty when filling the tank, as pressure builds and causes early shut off of the filler nozzle. Both valves shut off during a rollover event.
The ORVR valve may have a pressure relief valve, spring loaded in both directions for zero pressure in the tank and zero vacuum, that is vented to the atmosphere. A buzzing noise may be heard in hot weather conditions just as the engine is turned off. This is because the tank is being sealed under low pressure.
The primary purpose of this system is to route the fuel vapors that may escape from the filler neck during vehicle refueling into the EVAP canister. The canister absorbs these vapors and then purges them during driving.
Operation As the tank is refueled, a slight vacuum is created in the Signal Line by moving fuel at the top of the filler neck. This vacuum signal is applied to the top of the Refueling Control Valve by the Signal Line, which opens the Refueling Control Valve. The fuel entering the fuel tank creates a slight positive pressure in the tank, which causes the EVAP Vapor Cut Valve to open. With the Refueling Control Valve and EVAP Vapor Cut Valve open, fuel vapor can travel directly from the tank to the EVAP canister via the Refueling EVAP Vapor Line. The Recirculation Line minimizes the amount of fresh air pulled into the tank by recirculating the air in the tank, to the filler neck, and back to the tank.
Troubleshooting Most concerns about the ORVR system will be "slow-fill" concerns. A faulty ORVR valve can leak or cause difficulty when filling the tank, as pressure builds and causes early shut off of the filler nozzle. Some owners may experience difficulty 'filling their vehicles with gasoline and a premature shut-off condition due to the gas pump nozzles installed at their gas stations. The nozzles at these stations are in the process of being retrofitted or replaced by the nozzle manufacturers. In the meantime, owners should follow instructions posted near the gas pump and try filling the vehicle at a different gas station. If the refueling difficulty continues, verify that the 1/2" vapor path from the fill vent valve on the gas tank to the air filter on the charcoal canister is entirely free and clear. To perform the procedure below, ensure the fuel tank is below 1/4 tank full. To quickly determine the general location of a possible vapor path restriction, Disconnect the hose connected to the canister side of the liquid-vapor separator. Take the vehicle to a known "good" or major brand gas station. A. If the vehicle accepts fuel, the restriction is between the liquid-vapor separator and the air filter. B. The restriction is located between the liquid-vapor separator and the fuel tank if the vehicle does not readily accept fuel. After the restriction has been isolated to either half of the system, inspect each component to ensure it is free and clear of any restrictions. Verify that no back pressure can be felt anywhere between the fill vent valve and the air filter at the canister. All hoses and tubes for the ORVR System must be free and clear for proper operation. The ORVR lines are part of the EVAP system, so don't overlook them when diagnosing an EVAP leak concern. Blow through one end of the pipe using lung power when checking the liquid-vapor separator. NO back pressure should be felt. Please verify that the Fill Vent Valve is open by carefully removing the valve and confirming that the white plastic shut-off plunger moves freely inside its cage. A hard-to-fill condition may result if the Fuel Cut Valve plunger is stuck closed. Verify that the plunger moves up and down freely, allowing fuel to enter the tank but does not allow fuel to travel up the neck (under pressure). The plunger should be "up" (closed) in its free state. When working with the Fill Vent Valve and associated plumbing, replace the hoses with the proper hose clips to prevent fuel from getting trapped/puddled in the vapor hose. Return fuel from the liquid-vapor separator must have a clear path to drain back to the tank. Related DTCs: P0442 Small Leak P0456 Very Small Leak