Bad O2 sensor?

[1fastRS]

heres my problem, i put on a 3" cat back w/ a high flow cat. i also have a header. after driving the car for about 2 minutes my cel came on. i put out these codes:

PO138 - downstream heated O2 sensor fault (bank 1) <------ have no idea what bank 1 is.
PO139 - downstream O2 sensor stays at center
PO141 - downstream heated O2 sensor heater circut fault (bank 1)

what the hell does this mean? is my O2 sensor bad? can i use a O2 simulator and fix the problem or what. also out of no where my car has a horrible idle (goes back and forth from 800-600rpm) and when i drive it pops almost like a back fire but not as bad until about 3k, and then smooths out. while it does this it loses power. also if i'm driving and i upshift (ex. 4 to 3) if pops, and stalls before it goes. also if i'm crusing below 3k and i hit the gas it does the pop and stall thing. what the hell is it! i've been told that i'm running too lean. could this be from the O2 sensor? what else could cause it? i just changed my plugs today, and i'm changing the fuel filter and wires this week. please give me some other suggestions.

 

[luv2rallye]

Your rear O2 sensor has quit working. Replace it and watch 90% of your problems go away. Not sure about Bank 1 but it probably means something to the design engineers - don't worry about it.

 

[1fastRS]

so that definetely means my O2 is bad? also, my cel has been on for a few months
(thats when i put everything on), so why would i just now be experiencing these problems? its been running fine up until a few days ago.

 

[luv2rallye]

Yes your REAR (after cat under car) O2 sensor is bad. It may have been intermittent (so the ECU compensated but still threw a CEL) till now when it failed permanently (now the ECU doesn't know how to adjust mixture) so car runs like crap. Keep in mind you may also have other problems but you must definately take care of this (to even find any others).

 

[LightningGSX]

The sensor is unplugged or wires are cut, doesn't sound like the sensor is bad.

 

[luv2rallye]

That certainly is another possibility.

 

[LightningGSX]

The downstream o2(post cat) sensor is incapable of causing A/F problems, its purpose is to monitor the cat efficiency only.I would look for a clog in the cat or cat-back.

 

[1fastRS]

how could my cat or catback be plugged up already? and wouldnt that affect the car at all rpm levels, and not just areas of the rpm band?

 

[LightningGSX]

It was just a guess, these problems started when you put on the new exhaust correct?

Also I'm not sure how the EGR is setup on the N/Ts, but if you have less pressure in the exhaust manifold(from the 3" exhaust) ,than in the intake, EGR can flow the opposite way.Not sure if this is possible in your case though.