Standard Models (Non Bi-Fuel)
Evaporative Emission (EVAP) Systems
Overview
The EVAP system prevents fuel vapor build-up in the sealed fuel tank. Fuel vapors trapped in the sealed tank are vented through the vapor valve assembly on top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the EVAP canister for storage until the vapors are purged to the engine for burning.
All applications required to meet OBD regulations use the enhanced EVAP system. Some applications also incorporate an on-board refueling vapor recovery (ORVR) system.
Enhanced Evaporative Emission (EVAP) System
The enhanced 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 or vapor management valve (VMV) intake manifold hose assembly EVAP 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 or cylinder head temperature (CHT) sensor the intake air temperature (IAT) sensor the mass air flow (MAF) sensor the vehicle speed and the 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 leak check monitor based on the presence of vapor generation or fuel sloshing.
2. The PCM determines the desired amount of purge vapor flow to the intake manifold for a given engine condition. The PCM can then output the required signal to the EVAP canister purge valve or VMV. The PCM uses the enhanced EVAP system inputs to evacuate the system using the EVAP canister purge valve or VMV seals the enhanced EVAP system from the atmosphere using the CV solenoid and uses the FTP sensor to observe total vacuum lost for a period of time.
3. The 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 or VMV. On applications with electronic EVAP canister purge valve or VMV the PCM outputs a variable current (between 0 mA and 1000 mA).
5. The 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 and the 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 or VMV under any vehicle altitude handling or rollover condition.
7. The enhanced EVAP system including all the fuel vapor hoses can be checked when a leak is detected by the PCM.
Hardware
EVAP Canister Purge Valve
Note: The EVAP canister purge valve may also be referred to as a vapor management valve (VMV).
The EVAP canister purge valve is part of the enhanced EVAP system that is controlled by the PCM. This valve controls the flow of vapors (purging) from the EVAP canister to the intake manifold during various engine operating modes. The EVAP canister purge valve is a normally closed valve. The electronic EVAP canister purge valve controls the flow of vapors electronically by way of a solenoid thereby~ eliminating the need for an electronic vacuum regulator and vacuum diaphragm. The PCM outputs a signal between 0% and 100% duty cycle to control the EVAP canister purge valve. On applications with an electronic EVAP canister purge valve the PCM outputs a signal between 0 mA and 1000 mA to control the solenoid.
Fuel Tank Pressure (FTP) Sensor
The FTP sensor or in-line FTP sensor is used to measure the fuel tank pressure during the EVAP leak check monitor.
Canister Vent (CV) Solenoid
During the EVAP leak check monitor the CV solenoid seals the EVAP canister from the atmospheric pressure. This allows the EVAP canister purge valve to obtain the target vacuum in the fuel tank during the EVAP leak check monitor.
