System Operation - 3.0L Ho
PURGE FLOW OPERATION:
| A - Fuel Vapor Tube from Charcoal Canister |
| B - Purge Tube to Ejector Tee (Boost) |
| C - Purge Tube to Intake Manifold (Naturally Aspirated) |
| D - Vent Tube to OBD Vent Valve |
| E - Boost Line to Ejector Tee |
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. The vacuum in the intake manifold pulls check valve 3 closed blocking flow to the ejector tee. Fuel vapors are drawn from the canister, through the purge solenoid, and into the intake manifold through purge hose C.
- 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.
For information on how the Powertrain Control Module monitors and performs diagnostics on the system. Refer to EVAPORATIVE EMISSIONS PCM DIAGNOSTICS - TURBO .