Proportional Gain

What proportional gain does

Closed loop O2 control compares the wideband reading with your target and applies a short term fuel correction to close the gap. The proportional term scales that correction to the size of the error: a big miss gets a big correction, a small miss gets a small one. The proportional gain sets how aggressive that scaling is.

• Raise it and short term trim reacts faster and harder.
• Lower it and corrections are gentler and slower.
• Too high and the controller overshoots, corrects back, overshoots again, and the air-fuel ratio oscillates rapidly around the target.

It's one part of a three-term controller. The integral gain removes error that persists, and the derivative gain reacts to how quickly the error is changing.

The table and its axes

In NSP this is a table rather than a single number. It's laid out for engine load across the x axis (left to right) and RPM up the y axis (bottom to top), but either axis can be switched to any ECU channel if your application needs it.

To change the axis breakpoints, select the table and press F3, then edit an existing value or add a new one. When you move a breakpoint, NSP adjusts the cell values so the table keeps the same shape. You won't accidentally flatten your tuning by re-spacing the axis.

How we tune it

1. Get the fuel map reasonably close first. Gain should polish corrections, not do the tuning.
2. Start conservative, and log wideband reading, target and short term trim together.
3. Raise gain in an area until corrections settle quickly, then back off at the first sign of the mixture cycling rich-lean-rich.
4. Expect lower values at idle and light load, where sensor lag is long compared to how quickly the mixture changes, and more tolerance for higher values at higher load and RPM.

For the full picture of how short and long term trim work together, read our short and long term fuel trim guide and the O2 control setup.