What the table controls
A factory evaporative emissions (EVAP) system stores fuel vapor from the tank in a charcoal canister, then draws it into the intake through a purge solenoid to be burned. On a Nexus, the EVAP function drives that solenoid with a duty cycle. Higher duty opens it more and pulls in more vapor.
The O2 Inactive table sets the purge duty whenever the ECU isn't running closed loop fuel control, for example while the engine is warming up, at wide open throttle, or any time O2 feedback is switched off.
Why it's usually lower than the O2 Active table
Purge vapor is unmetered fuel. When closed loop fuel is active, the ECU sees the extra richness on the oxygen sensor and trims injector fuel to compensate, so the O2 Active table can safely use higher values. Without O2 feedback, nothing corrects for the vapor, and a heavy purge will simply make the engine run rich. That's why it's normal to see noticeably lower numbers in the O2 Inactive table.
How we approach it
- Start with the O2 Inactive values well below the O2 Active ones.
- Log lambda while the engine is open loop and the purge is running. If the mixture moves noticeably when the solenoid opens, reduce the duty.
- Use the coolant temp correction if you need to limit purging on a cold engine.
If you're wiring the solenoid for the first time, start with EVAP wiring.
