Evaporative Emissions

Evaporative Emissions

NOTE: The vehicle vacuum routing diagrams are contained in the Description and Operation subsection of the Engine Emission Control system. Refer to Emission Control Systems.

The Evaporative Emission (EVAP) system consists of the following components:

- Dust separator (located on the RH frame rail behind the fuel tank)
- EVAP canister (located on the top of the fuel tank)
- EVAP canister purge valve
- Fuel vapor vent valve (located on the RH frame rail behind the fuel tank)
- Fuel Tank Pressure (FTP) sensor (located on the top of the fuel tank)
- Vapor tubes
- Vapor hoses

The EVAP system:

- prevents hydrocarbon emissions from reaching the atmosphere.
- stores fuel vapors in the EVAP canister that are generated during vehicle operation or hot soak, until they can be consumed by the engine during normal engine operation.
- routes the stored fuel vapors to the engine during engine operation.
- is controlled by the PCM which, using various sensor inputs, calculates the desired amount of purge flow. The PCM regulates the purge flow, induced by the application of intake manifold vacuum, by varying the duty cycle applied to the EVAP canister purge valve.

The fuel vapors are routed:

- from the fuel tank through the fill limit vent valve and fuel vapor vent valve. The fuel vapor vent valves are part of the fuel tank assembly and cannot be serviced separately.
- to the EVAP canisters through a vapor line.
- to the engine when the EVAP canister purge valve is opened by the PCM.

The FTP sensor:

- monitors the pressure levels in the fuel tank.
- communicates the pressure reading to the PCM during the On-Board Diagnostic (OBD) II leak test.

The EVAP canister:

- is located on top of the fuel tank.
- contains activated carbon.
- stores fuel vapors.

Fuel tank filler cap (Explorer Sport Trac) and the Easy Fuel (TM) fuel tank filler pipe (Explorer/Mountaineer):

- relieves system vacuum below 3.8 kPa (15.26 in H2O).

The canister vent solenoid:

- is normally open.
- seals the EVAP system for the inspection and maintenance (I/M 240) test and OBD II leak and pressure tests.

The EVAP canister purge valve:

- is normally closed.
- regulates the purging of the EVAP canister.
- is electronically controlled by the PCM.

The dust separator:

- prevents suspended dust and dirt particles from entering the evaporative emission system.
- is serviced as a separate item.

The EVAP system monitor:

- is a self-test strategy within the PCM which tests the integrity of the EVAP system.
- monitors the EVAP system for leaks.
- monitors electronic EVAP components for irrationally high or low voltages.
- monitors for correct EVAP system operation.
- uses negative leak test methods to test and activate the EVAP system.
- has an engine malfunction light that will be displayed by the message center if the EVAP system fails the test.

The engine ON EVAP leak-check monitor:

- is executed by the individual components of the enhanced EVAP system. Intake manifold vacuum is utilized to reach a target vacuum on the EVAP system. The FTP sensor is used by the engine ON EVAP leak-check monitor to determine if the target vacuum necessary to carry out the leak-check on the EVAP system has been reached. Once target vacuum on the EVAP system is achieved, the change in EVAP system vacuum over a calibrated period of time determines if a leak exists.

The Engine Off Natural Vacuum (EONV) EVAP leak-check monitor is executed:

- once the engine ON EVAP leak-check monitor is completed and the key is turned OFF. The EONV EVAP leak-check monitor determines if a leak is present when the naturally occurring change in the fuel tank pressure or vacuum does not exceed a calibrated limit during a calibrated amount of time. A separate, low-power consuming microprocessor in the PCM manages the EONV leak-check. The engine OFF EVAP leak-check monitor is executed by the individual components of the enhanced EVAP system.