Enhanced Evaporative Emission (EVAP) System
Enhanced Evaporative Emission (EVAP) System
The Enhanced EVAP system (Figure 86) 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, powertrain control module (PCM) and connecting wires and fuel vapor hoses.
1. The Enhanced EVAP system uses inputs from the engine coolant temperature (ECT) sensor, the intake air temperature (IAT) sensor, the mass air flow (MAF) sensor, the vehicle speed sensor (VSS) and the fuel tank pressure (FTP) sensor to provide information about engine operating conditions to the PCM. The fuel level input (FLI) and FTP sensor signals to the PCM are used by the PCM to determine activation of the EVAP Monitor based on presence of vapor generation or fuel sloshing.
2. The PCM calculates a variable duty cycle based on the desired amount of purge vapor flow to the intake manifold for a given engine condition. The PCM can then output the duty cycle to the solenoid on the EVAP canister purge valve. The PCM uses the Enhanced EVAP system inputs to evacuate the system using the EVAP canister purge valve, seals the Enhanced EVAP system from atmosphere using the CV solenoid, and uses the FTP sensor to observe total vacuum lost for a period of time.
3. The canister vent (CV) solenoid seals the Enhanced EVAP system to atmosphere during the EVAP leak check Monitor.
4. The PCM outputs a variable duty cycle signal (between 0% and 100%) to the solenoid on the EVAP canister purge valve.
5. The 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.
6. 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 the Enhanced EVAP system to control the flow of fuel vapor entering the engine. All of these valves also prevent fuel tank overfilling during refueling operation and prevent liquid fuel from entering the EVAP canister and the EVAP canister purge valve under any vehicle altitude, handling or rollover condition. The liquid/vapor fuel discriminator is part of the fuel vapor control valve assembly on Escort and Focus applications.
7. The Enhanced EVAP system, including all the fuel vapor hoses, can be checked when a leak is detected by the PCM. This can be done by pressurizing the system using Rotunda Evaporative Emission Tester kit 134-00056 or equivalent and the leak (frequency) detector included with the kit.
Figure 86: Enhanced Evaporative Emission System (Refer To The On-Board Diagnostics II System Overview For Icon Definitions.):
