Ford 2003 Mustang Workshop Manual page 2149

Principles of Operation
Evaporative Emission (EVAP) Canister Purge Valve
The EVAP canister purge valve is controlled by the powertrain control module (PCM). The EVAP
canister purge valve controls the flow of fuel vapors from the EVAP canister to the engine intake
manifold during various engine operating modes. The EVAP canister purge valve is normally closed.
Evaporative Emission (EVAP) Canister
Fuel vapors from the fuel tank are stored in the EVAP canister. When the engine is running, the vapors
are purged from the EVAP canister for combustion.
Canister Vent Solenoid
During the Evaporative Emission (EVAP) System Test Monitor, Evaporative Emissions Repair
Verification Drive Cycle, and the Evaporative Emission System Leak Test, the canister vent solenoid is
closed to allow a vacuum to be drawn on the fuel tank at a specific level. The canister vent solenoid is
normally open.
Fuel Tank Pressure (FTP) Sensor
The fuel tank pressure sensor is used to measure the fuel tank pressure during the Evaporative
Emissions Monitor Test. The fuel tank pressure sensor is mounted in the fuel vapor control valve tube
as it crosses over the fuel tank.
Fuel Vapor Control Valve
The fuel vapor control valve is normally between the EVAP canister and the fuel vapor vent valve. Its
function is to prevent the flow of liquid fuel into the EVAP canister or up to the canister purge valve
during refueling, and to prevent the collection of liquid fuel in the fuel vapor hoses by overfilling the fuel
tank.
Fuel Vapor Vent Valve (FVV) Assembly
The fuel vapor vent valve (FVV) assembly is mounted on the top of the fuel tank. It is used to control
the flow of fuel vapors entering the EVAP system. The head portion of the assembly prevents the fuel
tank from overfilling during refueling. The assembly also has a spring float, which prevents liquid fuel
from entering the vapor delivery system under severe handling or vehicle rollover conditions. In the
upright position, the open bottom of the float will lift and shut off the orifice. Under severe handling
conditions, the spring will push the float closed when angles allow liquid fuel to reach the orifice. In a
rollover condition, the weight of the open bottom float and spring pressure will close the orifice.
Fuel Filler Pipe Check Valve
The fuel filler pipe check valve is an intricate part of the fuel filler pipe. It is intended to prevent liquid
fuel from re-entering the fuel filler pipe from the fuel tank on refueling or roll over conditions.
Fuel Filler Cap
The fuel filler cap is used to prevent fuel spill and to close the EVAP system to the atmosphere.
Evaporative Emission System Monitor
When a fault occurs, the EVAP system monitor is reset to NO and a diagnostic trouble code (DTC) is
set in the PCM memory. After the DTC is repaired, the vehicle drive cycle must be completed to reset
the monitor in preparation for inspection and maintenance testing.
EVAP Emission System Leak Test