Just got my magnaflow highflow cat put on today yeah so the guy said that this was going to mess up my rear 02 sensor and I might get a check engine light for it, cause it'* not used to reading the new backpressure....? hope i said that right. is there anything I can do about this? He said it might make it run a bit rich....

But my old cat was HOLLOW, like all the guts were completely burnt out so I'm gonna go ahead and figure that it can't run any richer than THAT one. ha.

The only reason that rear O2 sensor is even there is just to make sure the cat is working properly. It has nothing to do with engine management at all. Some other high flow cats might cause a SES light to be thrown but I've never heard of anyone having trouble with the Magnaflow cat including myself.

Ed

Can't see how the computer would think it has more or less backpressure as there are no pressure transducers in the exhaust system

Your rear o2 serves little purpose. It'* only function is to be a comparator to the front o2...if it gives the same readings as the front sensor, that tells the computer that the cat converter is shot. Otherwise, your rear o2 readings should constantly be lower than the front.

ya i had the shop tell me the same thing yesterday...

my cat is a magneflow stainless high flow 2 1/2 inches in and out and it half the size of the stock one .no code after 4 weeks good power

The code-throwing your installer was talking about when installing an aftermarket cat may have to do with the new cat being too small and/or too far away from the rear O2 sensor to adequately warm it up to operating temp. Since your rear O2 is of the electrically self-heating type, that'* not going to be a problem for you.

well that'* comforting, thanks!