What the table does
This table adjusts fuel based on atmospheric (barometric) pressure. Each cell holds a percentage change to fuel delivery for a given barometric pressure, so you can add or remove fuel as the air gets denser or thinner.
When you actually need it
It matters most on engines that use throttle position as the load input, common with individual throttle bodies. A TPS-based map only knows how far the throttle is open, not how much air is actually available. Drive up a mountain, or into a low-pressure weather system, and the same throttle angle lets in less air, so the engine runs rich. Barometric correction pulls fuel back to match.
On a speed density setup using a MAP sensor, the load reading already reflects some of the change, so any correction needed is usually small. Either way, the ECU needs a good baro reading from a barometric pressure sensor.
Setting it up
- Leave the cell at your usual local pressure at 0%. That's where the base map was tuned.
- For lower pressure (higher altitude), a TPS-load engine generally needs less fuel, so those cells go negative.
- Confirm with wideband logs whenever you're at a different altitude, rather than guessing big numbers.
For the other fuel adjustments, see fuel corrections and air temp correction.
