Evaporative Purge Control

Evaporative Purge Control is an output control function of the MS41.1 control module. As part of the "Running Losses/CARB" emission requirements, the MS41.1 purge control system must also be monitored for correct operation and leaks.

The system is redesigned from those currently in use with the Bosch DME management systems. Additional components have been added that allow the monitoring of leaks and more precise control of fuel tank vapors. The components of the purge system include:
- Charcoal Canister with integral Shut Off Valve
- Evaporative Purge Valve
- Fuel Tank Pressure Sensor (transducer)
- Liquid/Vapor Separator
- Vehicle Fuel Tank
- MS41.1 Control Module

The size of the Carbon Canister is increased from 0.75 to 3.0 liters. It's installed location is in the trunk, under the spare tire. The increased volume of the canister provides containment of a larger volume of HC vapors without allowing any loss to the atmosphere. Vapors that accumulate in the tank are allowed to pass from the tank through the liquid/vapor separator into the canister as in the past. The purge line is routed from the trunk, up to the engine compartment, through the purge valve and into the intake manifold.

A shut-off valve is installed on the intake or vent side of the charcoal canister. Operation of the valve is controlled by the MS41.1 control module. When the shut-off valve and purge valve are closed, the entire fuel tank is sealed from the atmosphere. The shut-off valve is required to test the system for leaks.










The purge valve is installed in the engine compartment below the Hot Film Air Mass Sensor.

As introduced with the DME M5.2 system, the purge valve is powered open. This ensures that the valve is closed when the engine is switched OFF, preventing vapors from escaping into the atmosphere.

The MS41.1 Control Module regulates the operation of the purge valve through a duty cycle control. The valve is cycled open based on engine RPM and Lambda regulation.

Purge control is shut down during idle and decel fuel cut-off.

The signal from the fuel tank pressure sensor is an input to the MS41.1 Control Module. Depending on the input value from the sensor, the MS41.1 Control Module can determine system operation and check for leaks.