o2 senser help etc.

[wftb]

i have a 2.2 ecotec with a home built turbokit .why do i have 2 o2 sensors?(one on the exhaust manifold and one downstream of the converter)do i need both? .when looking at my scans , which one is getting read? i have changed the injector constant to .13350 and this has helped hot starting .would that have changed my AFR ? is there a place where i can just input the AFR i want? i am getting a wideband tomorrow and i noticed some of them also send out a 0 to 1 volt signal so they can do double duty as stock as well . anyone have experience with this?i have had problems with oil contamination of my o2 sensors (turbo seals ) so i am hoping to kill two birds with one stone . the injector pulse width mult versus manifold vaccuum : is this a minus kpa value? i am assuming that anything higher than 0 kpa (+) will stay at a multiplier of 1 ? engine is from a 2003 cavalier .any help would be appreciated .thanks .

[wftb]

i guess i should add that i have HPT MPVI pro .

[nuttzzy]

the 2nd o2 is used to check teh effecency of the cat (correct me if im wrong) its a uni tasker thats all its for. that and to make dashlights come on when you modify your exhaust

[wftb]

thanks ,that makes sense .