Theory Of Operation

Courtesy of CHRYSLER GROUP, LLC

GENERAL OPERATION:  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 and the pressure on the other side of the check valve forces 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 opens check valve 3 allowing boost pressure through the manifold boost pressure tube (E) 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. The vacuum created inside the Purge Solenoid along with the boost pressure in the Intake Manifold purge tube (C) forces check valve 1 closed. 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.

PURGE FLOW MONITOR:  The Powertrain Control Module (PCM) detects leaks in the Evaporative system when the Purge Solenoid is closed. Therefore it cannot determine if hardware between the Purge Solenoid and Intake Manifold is damaged or leaking during leak testing. The Purge Flow Monitor is needed to determine if the engine side of the system is connected and functioning properly. This is done by monitoring the Fuel Tank Pressure (FTP) Sensor signal for a delta (change) of more than a calibrated threshold in the signal when the Purge Solenoid is energized.

The Purge Flow Monitor will only run if the Small Leak Monitor recorded a pass on the previous ignition off event and the test data was valid. The boost portion of the monitor will only run when there is a sustained stable boost condition and not when the vehicle is at wide open throttle. The PCM runs the Purge Flow Monitor once per drive cycle for both engine operating modes and both diagnostics will run during the drive cycle if the parameters allow regardless if the first diagnostic fails.

• When the Purge Flow Monitor begins to run the normally closed OBD Vent Valve is briefly opened to vent the system to atmosphere. After the Purge Solenoid is energized the PCM monitors the FTP Sensor pressure delta to determine a pass/fail.
• If the diagnostic fails when the engine is running in naturally aspirated mode, the PCM will set the (P0441)  DTC.
• If the diagnostic fails when the engine is running in boost mode, the PCM will set the (P1CEA)  DTC.