O2/boosting problem Options

[90GSX]

Ok my car has been throwing a C/E light for some time, well it comes on for a few days, goes off for a few days, and so on. Well for a while now i have felt a powerloss from when i bought the car it seems. My factory boost guage only is reading 4-5 PSi and never any higher. Well after playing with my pocketlogger, the light says its code 11 O2 sensor. Does that mean its bad or is something else making it read wrong? I logged a run and the front o2 reads 2.5v all the time, never changes. the rear o2 read 0.00v-0.13v peak on a run. I get about 43 counts of knock about 6500-7k RPM, it reads ~0 till i hit 3k-3500 rpm. My car is totally stock, and i checked the piping and dont see any visible leaks and my question is will a bad o2 make you loose boost and is the o2 sensor itself bad? They are 118 bucks for a new one so i wanted to cover all other options before i got a new one. I have 176k miles, and i know at one point the previous owner replaced it already, but i dont remember when, i will have to check the paperwork. any help will be appreciated. Oh and another thought of a boost leak would be it might possibly be leaking into the crankcase, the dipstick pops out sometimes and also the "breather" completely comes out also. My oil pressure reads about a quarter inch from the 2nd line on the guage when i get on it, i have a feeling that probably isnt accurate considering the miliage. Anyone got any ideas? thanks

[90GSX]

yeah is for the 90 gsx. I was assuming it was possible to leak boost through the turbo into the crankcase though the oil return line. Maybe i was wrong. The oil pressure i assume would be good if its close to that second line, but surprising with the miles i do have. The 2 other DSMs i had never got that good. my laser barely gets above the first line. I went to advance auto to price the o2, they have been the cheapest i have found on stuff for my car, i havent priced autozone yet. I thought i only had 1 o2, i dont know why my logger is getting a reading for an o2-r . im using MMcd logging software with a palm m/105 . the o2-f reads 2.50v and never moves. As for the 43 counts of knock, if thats the case, doesnt the ECU pull the boost back if it reads that much knock? Im a big newbie here. Ive been trying to follow posts here for almost 2 years before i finally got my turbo car. Ive been made aware not to trust the factory boost gauge, and i am on the lookout for an aftermarket gauge and pod (dual or tripple) if anyone has one for sale. I would just buy new, but im still paying on it so money is alittle tight at the moment, and i need a new exhaust anyways. Stock definatly sounds horrible. Gas miliage wise, im running about 24 mpg with a fair share of highway driving and in town driving and (getting on it to hear the turbo) hehe. So i dont know if im really running that rich or not, but imo the car doesnt feel as spunky (i guess i can put it like that) as it did when i bought it a couple months back, so thats kinda how im guessing my boost isnt where its supposed to be, even for stock.