Not sure what wide vs narrow band means - ok looked this up and follow now.

I downloaded the instructions for the unit Philip posted the link for and it requires a boss to be welded into the exhaust to fit the sensor to then read the mixture

So if I install that I can then read the mixture at idle, coasting, acceleration, cruising etc and then adjust the fuel rail pressure to change that?

Hmm tempting to learn how to do all this. I note I would have to remove the sensor when not using it to read the mixture - inserting a plug in the boss.