Since you like to help people via questions here is an easy one for you or anyone else who wants to have a shot, its pretty simple
Whats closed loop mode in a engine control unit in relation to injection/ignition

In closed loop the ECU looks at the oxygen sensor to determine the injector flow.

:stoopid:

pretty much what he said.. in closed loop the ECU measures the output of the oxygen sensor to see if the car is running a stoichiometric air-fuel ratio (which for ULP is 14.7:1) and if it isn't then it adjusts injection and ignition until it is.

and then, to complicate things slightly, you have narrow-band and wide-band oxygen sensors. Narrow-band is the standard fit, but will only register in a narrow range of AFR values around 14.7 - okay for the majority of engines.

But once you get into serious mods, a wide-band O2 sensor becomes an asset - at a cost of over $200, I hear.

But once you get into serious mods, a wide-band O2 sensor becomes an asset - at a cost of over $200, I hear.
You only need a wide-band for tuning purposes. While the car is running, a narrow-band version is just fine.

most o2 sensors are only a trim they dont have to hooked up but your fuel econ goes to crap they dont sit on 14.7 they normily move between 13.7 and 15.7 if u give ya motor a boot the tps and air flow meter tell comp that u want fuel so comp opens the injection pulse wider so injectors stay open for longer the o2 only trims the mixture and normily on cruse some 4 wire o2 sensors need to be hooked up or you get a realy bad flat spot .

Question #2:

Guess what happens when you get an exhaust leak at the header flange.....

o2 gives comp lean mixture so comp open injection pulse more fuel goes in and fuel consumption goes to crap

Bingo.