Emission System Overview

EMISSION SYSTEM

EMISSION SYSTEM 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.

ENHANCED EVAPORATIVE EMISSION (EVAP) SYSTEM
The enhanced EVAP system consists of
- a canister vent (CV) solenoid
- EVAP canister
- EVAP canister purge valve
- fuel tank
- fuel tank isolation valve (FTIV)
- fuel filler cap, fuel vapor control valve
- fuel vapor vent valve
- fuel tank pressure (FTP) sensor
- intake manifold hose assembly
- powertrain control module (PCM)
- connecting wires
- and fuel vapor hoses.






1. The enhanced EVAP system uses inputs from the cylinder head temperature (CHT) sensor, the intake air temperature (IAT) sensor, the mass air flow (MAF) sensor, the vehicle speed 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 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 then outputs the required signal to 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 the atmosphere using the CV solenoid, and uses the FTP sensor to measure the total vacuum lost for a period of time.






3. The CV solenoid seals the enhanced EVAP system from the atmosphere during the EVAP leak check monitor.
4. The PCM outputs a variable duty cycle signal (between 0% and 100%) and a variable current (between 0 mA and 1000 mA) to the solenoid on the EVAP canister purge valve.
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 are used in the enhanced EVAP system to control the flow of fuel vapor entering the engine. 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.
7. The FTIV isolates the fuel tank from the rest of the EVAP system when the vapor flow is required only from the EVAP canister, and not from the fuel tank.

The enhanced EVAP system, including all the fuel vapor hoses, can be checked when a leak is detected by the PCM.

EVAPORATIVE EMISSION (EVAP) CANISTER PURGE VALVE
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 variable duty cycle signal (between 0% and 100%) and a variable current (between 0 mA and 1000 mA) to the solenoid on the EVAP canister purge valve.






EGR SYSTEM OVERVIEW
The Exhaust Gas Recirculation (EGR) system returns a small amount of exhaust gas into the intake manifold. This reduces the overall combustion temperature. Cooler combustion temperatures provide a significant reduction of the oxides of nitrogen (NOx) in the exhaust emissions.

The engine incorporates a stepper motor-controlled EGR valve which receives its signal from the PCM. Engine coolant is used to cool the EGR valve. The EGR valve and stepper motor are serviced as an assembly.

The amount of recirculated exhaust gas depends on:
- engine rpm.
- intake manifold vacuum.
- exhaust backpressure.
- engine coolant temperature.
- throttle position.

ELECTRIC EGR (EEGR) SYSTEM
- The EEGR valve is activated by an electric stepper motor and does not use vacuum to control the physical movement of the valve.
- No DPFE sensor is used.
- No orifice tube/assembly is used.
- A manifold absolute pressure (MAP) sensor.
- Engine coolant is routed through the EEGR assembly extending the durability of the electric motor.






EEGR SYSTEM OPERATION
- The EEGR system receives signals from the cylinder head temperature (CHT) sensor, the throttle position (TP) sensor, the mass air flow (MAF) sensor, the crankshaft position (CKP) sensor and the MAP sensor to provide information on engine operating conditions to the PCM. The engine must be warm, stable, and running at a moderate load and RPM before the EEGR system is activated. The PCM deactivates the EEGR during idle, extended wide open throttle (WOT), or whenever a failure detected in an EEGR component or an EGR required input.
- The PCM calculates the desired amount of EGR for a given set of engine operating conditions.
- The PCM outputs signals to the EEGR motor to move (advance or retract) a calibrated number of discrete steps. The electric stepper motor directly actuates the EEGR valve independent of engine vacuum. The EEGR valve is commanded from 0 to 52 discrete steps to get the EGR valve from a fully closed to fully open position. The position of the EGR valve determines the EGR flow.

EEGR VALVE
The EEGR valve is a water-cooled motor/valve assembly. The motor is commanded to move in 52 discrete steps as it acts directly on the EEGR valve. The position of the valve determines the rate of EGR. The built-in spring works to close the valve against the motor opening force.