Description And Operation - Turbo: Notes
DESCRIPTION
The Evaporative Emissions system consists of the following components:
| EVAP SYSTEM COMPONENTS | |||
|---|---|---|---|
| CALLOUT | DESCRIPTION | CALLOUT | DESCRIPTION |
| 1 | Refer to CANISTER FRESH AIR FILTER . | 15 | Refer to INTERNAL TANK VENT VALVES . |
| 2 | Filter Hose (Filter to ESIM) | 16 | Fuel Tank |
| 3 | Refer to EMISSION SYSTEM INTEGRITY MONITOR (ESIM) . | 17 | Purge Tube (Purge Solenoid to Canister) |
| 4 | Refer to CHARCOAL CANISTER . | 18 | OBD Vent Valve Tee |
| 5 | Gas Cap or Cap-less Refueling Unit (if equipped) | 19 | Refer to OBD VENT VALVE . |
| 6 | Recirculation Tube (metal portion) (FTPS to Fuel Filler Tube) | 20 | OBD Vent Valve Filter |
| 7 | Fuel Filler Tube | 21 | Refer to EVAPORATIVE EMISSIONS PURGE SOLENOID . |
| 8 | Refer to FUEL TANK PRESSURE (FTP) SENSOR . | 22 | Evaporative System Turbocharger Tee |
| 9 | Grade Vent Valve (GVV) | 23 | Check Valve 2 (to the Turbocharger) |
| 10 | Hose - Fuel Filler Tube to ICV | 24 | Check Valve 1 (to the Manifold) |
| 11 | Inlet Check Valve (ICV) | 25 | Refer to EJECTOR TEE . |
| 12 | GVV Tube (GVV to MFCV) | 26 | Hose to the Airbox Side of the Turbocharger |
| 13 | Recirculation Tube (Fuel Tank to FTPS) | 27 | Hose to the Charge Air Cooler Side of the Turbocharger |
| 14 | Canister Tube (Fuel Tank to Canister) | 28 | Manifold Hose (Purge Solenoid to Engine Manifold) |
| CALL OUT | DESCRIPTION |
|---|---|
| 1 | Purge Solenoid |
| 2 | One-Way Check Valve |
| 3 | OBD Vent Valve |
| 4 | One-Way Check Valve |
The Evaporative Emissions (EVAP) purge solenoid (1) is located in the engine compartment attached to the intake manifold support bracket and held in place with a rubber grommet.
OPERATION
EVAP SYSTEM OPERATION: The Evaporative Emissions System is designed to manage fuel vapors. The Powertrain Control Module (PCM) monitors the performance of the Evaporative Emission System. The system uses the principle of Natural Vacuum Leak Detection (NVLD) to determine the integrity of the system. When fuel vapors build and exit the Fuel Tank they are routed and stored in the Charcoal Canister. Fuel vapors entering the Charcoal Canister are absorbed by the charcoal filter until they can be drawn into the Intake Manifold during purging and burned by the engine.
The two main areas being monitored are the integrity of the system against leaks and the ability of the system to purge fuel vapor from the canister to the Intake Manifold.
- The basic strategy used for leak testing is that in a sealed system , pressure will naturally increase or decrease in relation to temperature. The Evaporative System Integrity Monitor (ESIM) Switch is used for all leak fault detection. There is a vacuum actuated switch that closes when the vacuum reaches a calibrated threshold. If the switch closes it indicates that the system is not leaking.
- The basic strategy used for purge performance testing is that as flow through the system increases, so does the pressure drop in the system. The Fuel Tank Pressure (FTP) Sensor is used for purge fault detection. The PCM monitors the Fuel Tank Pressure Sensor and looks for increasing vacuum in the Fuel Tank with increasing purge flow. Conversely, it looks for decreasing vacuum in the Fuel Tank with decreasing purge flow.
PURGE FLOW OPERATION
While the leak detection principle is the same on the Turbocharged engine as it is on the Naturally Aspirated engines, the purge system operation and diagnostics are different. The Turbocharged engine requires the ability to draw fuel vapors from the Charcoal Canister during both Naturally Aspirated operation and during boost conditions. Typically engine vacuum is used to draw the fuel vapors from the canister. This is easily accomplished on a naturally aspirated engine that has sufficient vacuum in the Intake Manifold during most engine operating conditions. It is more difficult when a Turbocharged engine is in boost mode creating positive pressure in the Intake Manifold. This is accomplished using a different Purge Solenoid than is used on non-Turbo engines along with some additional hardware. The function of the purge system in each mode of operation is as follows:
- Naturally Aspirated: When the Purge Solenoid is energized the vacuum from the Intake Manifold pulls check valve 1 open. The vacuum created inside the Purge Solenoid pulls check valve 2 closed, sealing it off to the Ejector Tee. Fuel vapors are drawn from the canister, through the Purge Solenoid, and into the Intake Manifold.
- Boost: When the Purge Solenoid is energized the pressure in the Intake Manifold closes check valve 1 and opens check valve 3 allowing airflow to the Ejector Tee. The airflow through the Ejector Tee creates a venturi effect creating vacuum in the line between the Purge Solenoid and Ejector Tee, pulling check valve 2 open. Fuel vapors are drawn from the canister, through the Purge Solenoid, and into the Air Cleaner box where they travel with the intake air to the Intake Manifold.