Enhanced Evaporative Emission System: Notes
The enhanced Evaporative Emission (EVAP) system consists of a fuel tank, fuel filler cap, fuel tank mounted or in-line fuel vapor control valve, fuel vapor vent valve, EVAP canister, fuel tank mounted or fuel pump mounted or in-line Fuel Tank Pressure (FTP) sensor, EVAP canister purge valve, intake manifold hose assembly, Canister Vent (CV) solenoid, PCM and connecting wires and fuel vapor hoses. The following list of components and their specific operation corresponds to numbers in illustration. See Fig 1.
- Enhanced EVAP system uses inputs from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Mass Airflow (MAF) sensor, Vehicle Speed Sensor (VSS) and Fuel Tank Pressure (FTP) sensor to provide information about engine operating conditions to PCM. The Fuel Level Input (FLI) and FTP sensor signals are used by PCM to determine activation of EVAP Monitor based on presence of fuel vapor or fuel sloshing.
- PCM calculates a variable duty cycle based on desired amount of purge vapor flow to intake manifold for a given engine condition. PCM can then output the duty cycle to solenoid on EVAP canister purge valve. PCM uses Enhanced EVAP system inputs to evacuate system, using EVAP canister purge valve, CV solenoid to seal Enhanced EVAP system from atmosphere, and uses FTP sensor to observe total vacuum lost for a period of time.
- Canister Vent (CV) solenoid seals EVAP canister from atmospheric pressure. See Fig 2. This allows EVAP canister purge valve to obtain fuel tank target vacuum during EVAP Leak Check Monitor.
- PCM outputs a variable duty cycle signal (between zero and 100 percent) to solenoid on EVAP canister purge valve. For additional EVAP canister purge valve information, see EVAP CANISTER PURGE VALVE .
- Fuel Tank Pressure (FTP) sensor monitors the fuel tank pressure during engine operation and continuously transmits an input signal to the PCM. During the EVAP monitor testing, the FTP sensor monitors the fuel tank pressure or vacuum bleed-up. See Fig 3 and Fig 4 .
- The fuel tank mounted fuel vapor vent valve assembly, fuel tank mounted fuel vapor control valve (or remote fuel vapor control valve) are used in Enhanced EVAP system to control flow of fuel vapor entering engine. All of these valves also prevent fuel tank overfilling during refueling operation and prevent liquid fuel from entering EVAP canister and EVAP canister purge valve under any vehicle altitude, handling or rollover condition. The liquid/vapor fuel discriminator is part of fuel vapor control valve assembly on Focus and ZX2 models.
The Enhanced EVAP system, including all fuel vapor hoses, can be checked when a leak is detected by PCM. This can be done by pressurizing system using Rotunda Evaporative Emission Tester Kit (134-00056) or equivalent, and leak (frequency) detector included with kit.