S15 running lean

[Kingtal0n]

Originally Posted by Dboyizmlg

Your highway mileage is really good compared to mine, that's for sure!

I have small stage 1 cams on mine so city isn't bad, I would say 18-22mpg city.

What really improved highway mileage is timing. You need at LEAST 36 btdc cruising. I would shoot closer to 38 or 39.

When it was at 31* mileage was much worse, like 23mpg.

I spent a long time data-logging to figure this out. its pretty simple though, you just log injector duty cycle and fuel pressure for a lloooooong time. and add timing slowly. If your chart slowly gradually drops off in duty cycle and engine vacuum improves (fuel pressure is seen to drop) you are using less and less fuel at the same speed. cruise control helps.