More Fuel Trim!
My small suggestion is that you increase the range that the fuel trim can go and stick 14.7 exactly in the middle of the gauge where it belongs.
Possibly making the max 30:1 and the minimum 1:1. The reason is now a days with direct injection we can have cars go up to 18:1 AFR (Air Fuel Ratio) and I think there is even a car that goes to 21:1.... So if in this game we want cars that are super fuel efficient we can achieve it and as for the rich side, If we just want a fuel sucking beast that would be pretty fun too.