Bad O2 Sensor or Bad Cat?
Thread Starter
Launching!
Joined: Feb 2005
Posts: 272
Likes: 0
From: Southern California
Bad O2 Sensor or Bad Cat? I put the Random Tech Catted y-pipe on my T/A 18mos ago. About a month ago I hit the gas hard and the car popped and a big puff of smoke shot out the tail pipes. After that I noticed that I could smell a lot of gas in the exhaust and it soundslike there's an exhaust leak. Also, I was told that small black puffs of smoke shot out the tail pipes at every shift under WOT. My gas mileage sucks now, so I hooked the scanner to it. Both the O2 sensors on bank 2 were reading all over the place. Could my cat be bad? And is it about time to switch my O2 sensors? Or is there something else wrong? It's driving me nuts! 
I can't imagine that the cat would go bad after only 18mos unless the O2 sensors died, but I'm stumped, especially since the scanner showed that it bank 2 was alternating between running lean then rich. 
Thanks for the help.
I can't imagine that the cat would go bad after only 18mos unless the O2 sensors died, but I'm stumped, especially since the scanner showed that it bank 2 was alternating between running lean then rich. Thanks for the help. 
I would change both O2 sensors because they should read steady around 600 or 700. And when O2 go bad, they run really rich which would explain the bad mileage. There is a possibility it could be a cat but according to your scanner, it seems to be O2.
Thread Starter
Launching!
Joined: Feb 2005
Posts: 272
Likes: 0
From: Southern California
I changed both pre-cat O2s and my mileage seemed to have gone back up. However, when I ran it on the sniffer again it blew dirty. After looking at the long term feul curve it showed that it's still slurping more gas than it should be. The O2 sensors were definitely working better, but I think I have another problem. Need more tuning or need a new cat(s)??? This is driving me nucking futs!!!
