Component Description

EVAP/PURGE SOLENOID
The duty cycle EVAP purge solenoid regulates the rate of vapor flow from the EVAP canister to the throttle body. The Powertrain Control Module (PCM) operates the solenoid.

During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged.

When purging the PCM energizes and de-energizes the solenoid approximately 5 or 10 times per second, depending upon operating conditions. The PCM varies the vapor flow rate by changing solenoid pulse width. Pulse width is the amount of time the solenoid energizes.

FUEL FILLER CAP
If the filler cap needs replacement, only use a similar unit.

Fig. 4 Pressure Vacuum Filter Cap:

The fuel filler tube cap seals the fuel tank when threaded onto the filler neck. For safety, the cap contains pressure-vacuum relief valves. A malfunction in the system or damage to the fuel lines could cause excessive fuel tank pressure. The relief valves prevent possible excessive pressure or vacuum build-up in the fuel tank.

Removing the cap breaks the seal, relieving fuel tank pressure.

Fig. 8 ORVR System Schematic:

ORVR
ORVR System Schematic and components.

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. 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 reciculation tube.

Fig. 9 EVAP Canister And Leak Detection Pump:

VAPOR CANISTER
All vehicles use a sealed; maintenance free, charcoal filled EVAP canister. The canister mounts to the radiator support behind the front fascia.

All vehicles use a maintenance free, evaporative (EVAP) canister. Fuel tank vapors vent into the canister. The canister temporarily holds the fuel vapors until intake manifold vacuum draws them into the combustion chamber. The Powertrain Control Module (PCM) purges the canister through the proportional purge solenoid. The PCM purges the canister at predetermined intervals and engine conditions.

Purge Free Cells
Purge-free memory cells are used to identify the fuel vapor content of the evaporative canister. Since the evaporative canister is not purged 100% of the time, the PCM stores information about the evaporative canister's vapor content in a memory cell.

The purge-free cells are constructed similar to certain purge-normal cells. The purge-free cells can be monitored by the DRB III Scan Tool. The only difference between the purge-free cells and normal adaptive cells is that in purge-free, the purge is completely turned OFF. This gives the PCM the ability to compare purge and purge-free operation.