Gasoline in the tank constantly gives off vapor. On a factory emissions system, that vapor is trapped in a charcoal canister instead of being vented to the air. A purge solenoid between the canister and the intake then lets the engine draw those vapors in and burn them. The EVAP (Evaporative Emissions Control) function on a Nexus ECU operates that purge solenoid, so a street car can keep a working emissions system after the swap.
How the ECU controls it
The solenoid is driven with a PWM signal. The duty cycle decides how much vapor flows: low duty lets a trickle through, higher duty opens the path further. The ECU then adjusts that duty with corrections like coolant temperature and fuel tank pressure.
Frequency
The one setting on this node is Frequency, how fast the solenoid is pulsed. Purge solenoids want a very slow signal, usually somewhere from 2 to 20 Hz. That slow pulsing is what lets the valve meter small amounts accurately, from fully shut up to a modest flow. If you know the factory frequency for your solenoid, use it.
Purged vapor is extra fuel the ECU didn't inject. If your idle or light cruise mixture wanders when purge is active, look at your purge duty and corrections before touching the fuel map.
Wiring the solenoid is covered in EVAP wiring.
