Nothing makes sense. No consistency in the tune $8D mask

[Turbo Nasty]

So I made it to dyno day and everything was running great, however the next time I drove it in Closed Loop it was way too lean! It was off the scale of my AEM UEGO wideband and undriveable. As of right now I can only drive it in Open Loop and it runs like a champ in Open Loop. Later that day my alternator quit and was replaced and then my plastic brake booster cracked causing a vacuum leak and no power brakes. I have a metal one on order. This stuff may not have anything to do with my tuning issues but I though I should mention it.

[Xnke]

If closed loop is lean, but open loop is OK, suspect your oxygen sensor wiring or the sensor itself, OR you have an exhaust leak upstream of the sensor. O2 sensors do not measure fuel-they only measure oxygen.

That means if you have an exhaust leak upstream of the sensor, it'll pull in some fresh air-which means the O2 sensor will see oxygen, and it will report lean-because as far as it knows, that oxygen made it through the combustion process and didn't get burned-so all the fuel was burned with leftover O2. LEAN! Except, of course, you're not really lean because the excess oxygen came in through the exhaust leak-not through the combustion chamber.

False leans on the sensor would result in overfueling and the engine running rich, but reporting lean. This kind of thing can make you pull your hair out-so make sure you have no exhaust leaks up stream of the O2 sensor.