Question about O2 Sensor mods

[gto78]

I recently bought a 2003 Ford Expedition which we use for camping trips. The mileage is not bad for a 5,600 pound vehicle but it could definitely be better. I know it needs new O2 sensors since the previous owner had the worst maintenance I've ever seen. On my laptop the O2 sensors are very slow reacting unless your cruising on the highway, but at low speeds they aren't hot enough or something and they don't give good readings like new sensors. They have 139,000 miles on them.

When I replace them, I'm thinking of working with them a little bit to peak out the mixture slightly more. I have a dual EFIE box that I used on my explorer.

My question first is: Does higher voltage from the O2 mean leaner or richer? Also I know it's a 4 wire heated sensor, but what "Type" is it? I keep reading about zirconia and planar and some other types that either create their own voltage or use a reference voltage. But so I understand it better, I need to know what type I have.

I've read one article saying to wrap the O2 sensor and surrounding pipe with tin foil and heat wrap, to make it hotter which supposedly tells it to give less fuel. (sounds backwards to me) Then I read another article saying to use spark plug anti-fouler to extend the O2 sensor away from the pipe causing it to be cooler, which they say tells the computer to burn less fuel..... the two articles completely contradict each other.