Evaporative Emissions
WARNING: This page is about a different car, the 2008 Ford RV Cutaway, 2008 Ford Econoline, 2008 Ford E450 Super Duty, and 2008 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
The vehicle vacuum routing diagrams are contained in the Description and Operation subsection of the Engine Emission Control part. Refer to ENGINE EMISSION CONTROL
article.
The evaporative emission (EVAP) system consists of the following:
- Dust separator
- EVAP canister
- EVAP canister bracket
- EVAP canister vent solenoid (if equipped)
- EVAP canister purge valve
- EVAP hydrocarbon filter canister
- Fuel tank pressure sensor
- Fuel vapor vent valve
- Vapor hoses
- Vapor tubes
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 uses various sensor inputs to calculate the desired amount of EVAP purge flow. The PCM regulates the purge flow, induced by the application of intake manifold vacuum, by varying the duty cycle applied to the canister purge valve.
The fuel vapors are routed:
- from the fuel tank through the fuel vapor vent valves.
- to the EVAP canister 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 OBD II leak test.
The EVAP canister:
- is located along the LH frame rail for vehicles with rear fuel tanks or on the rear crossmember for vehicles with a midship fuel tank.
- contains activated carbon.
- stores fuel vapors.
The fuel tank filler cap:
- relieves system vacuum below 3.5 kPa (15.09-in H2 O).
The EVAP canister vent solenoid:
- is normally open.
- seals the EVAP system for the OBD II leak and pressure tests.
- is mounted to the EVAP canister.
- is repaired as a separate item.
The EVAP canister purge valve:
- is normally closed.
- regulates the purging of the EVAP canister.
- is controlled by the PCM.
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 Evaporative Emission (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 Engine Off Natural Vacuum (EONV) leak-check. The engine OFF EVAP leak-check monitor is executed by the individual components of the enhanced EVAP system.