The main fuel table sets fueling for the engine as a whole. The Cylinder correction tables sit on top of that and let you add or remove fuel for one cylinder at a time. Each cylinder has its own table, so the correction can vary across the operating range instead of being a single fixed number.
Why cylinders need different fuel
- Injector differences. Even a matched set of injectors varies a little in flow.
- Intake manifold design. Runners at the end of a plenum often breathe differently from those in the middle.
- Anything else uneven in how air or fuel reaches each cylinder, such as fuel rail layout.
If some cylinders run leaner than others, the leanest one sets how far you can safely push the tune. Balancing them lets the whole engine run closer to its ideal mixture.
How we use it
You need a way to see each cylinder's mixture before correcting it. Individual exhaust gas temperature sensors on each runner are the common method, and per cylinder wideband sensors are better again. With the engine running steadily at a given load, compare the readings and trim the outliers a small amount at a time. Get the main fuel table right first, since per cylinder trims are for fine balancing, not fixing a bad base map.
See the other fuel corrections, such as air temp and coolant temp correction, and our wideband O2 setup page.
