1978transam

I know that these codes are talking about the rear O2 sensors but I have just changed all 4 O2 sensors and I am still getting this code when I have it at WOT. I know when I bought the car I took it in and the mechanic told me that a pipe had a hole in it but it was very common and he know what to do for a quick fit. I think it is that part that is giving me problems but I don't know what part that is. Has anyone else had this problem or knows what part the mechanic was talking about?Thanks,

Avaric3

iTrader: (3)

it sounds like the problem is your catalytic converters. that may be the part hes talkin about. cuz that would trip the check engine light thru your back sensors. unless you just have a big enough exhaust leak to throw off the air gettin to the sensors