Evaporative Emission Purge Valves

The M73 engine has one purge valve per cylinder bank controlled by the respective DME control module. The function of the valve has changed from previous systems. The new valve will also be carried over to other engines.

The valve is normally closed and powered open. The valve seat is held closed by spring pressure. This new purge valve is required for the IM 240 tests. The valve will not open under fuel vapor over pressure.

The O2 sensors detect the additional rich mixture when the DME opens the purge valves. The valves are cycled periodically during engine operation.

Full Throttle = Purge Valve fully open. Solenoid pulsed at 95% duty cycle. Engine conditions are low intake manifold vacuum.

Warm Idle = Purge Valve slightly open.

Decel / Cold Idle = Purge valve closed. No solenoid activation. Engine conditions are high intake manifold vacuum.

The duty cycle of the purge valve solenoids may vary between 0 and 100% depending on engine operating conditions.