Purge Valve

The ECM (Engine Control Module) will not operate the EVAP (Evaporative Emission) purge process until the engine coolant temperature is above 55°C (131°F) and closed loop fueling is operational. Under these conditions the engine will be running smoothly with no warm up enrichment.

The purge valve duty cycle (and vapor flow) is initially increased slowly because the vapor concentration is unknown and a sudden increase in purged vapor could cause unstable engine running or cause it to stall due to an extremely 'rich' air/fuel mixture.

When the purging process is active, fresh air is drawn into the EVAP canister via the canister vent port on ROW vehicles or via the DMTL (Diagnostic Module Tank Leakage) filter and pump on NAS vehicles.

The purge valve is located on the left side of the engine, below the ignition coils cover. The purge valve is a solenoid operated valve which is closed when de-energized.

A vapor pipe is routed from the purge valve to the inlet of the supercharger. The purge valve is controlled by the ECM (Engine Control Module) and is operated when the engine operating conditions are correct to allow purging of the EVAP (Evaporative Emissions) canister.

A vapor pipe, which is routed parallel with the fuel delivery pipe along the left underside of the vehicle, connects the purge valve to the EVAP canister.

The purge valve is operated at 10 Hz by a PWM (Pulse Width Modulation) control ground from the ECM. The purge valve receives a fused power supply from the EJB (Engine Junction Box). At this high frequency, pulses of fuel vapor flow into the intake of the supercharger in an almost continuous flow. The valve operates at a duty cycle of between 7% and 100%.

Atmospheric pressure in the EVAP canister is higher than the pressure at the supercharger inlet under all throttle settings and engine running conditions. This pressure differential allows vapor to be drawn from the EVAP canister, through the open purge valve and into the supercharger air intake.