Air Fuel Ratios/mixture

[99350]

This is a question that may be kinda dumb. But when tunning how do you know what the air fuel ratios are when tunningg. We use a wideband for tunning gas motors. Do you just base it off of EGT's or what. Will a wideband O2 be able to work at all with a diesel, i know some of the gasses output by a diesel are different. This is just new to me and I would like to have some ideas before I do anything. Another thing why is it that some tuners like tto have diesels bellowing out a ton of smoke where as others can make similar power levels without as much smoke, is there a benifit to a whole lotta fuel.

I will be purchasing the tuner soon and I have access to a dyno and "open roads" to du some live tuning/testing.