o2 sensors & ses light

[v6guam]

My 3.4 has 104,000 miles on it and I'm pretty sure the o2 sensors are bad. The car was running rich and I was getting a light. Now, I have unplugged both sensors and the car runs much better and I don't get a SES light. Can anyone tell me why this is happening?

[94Redbird]

When was the car running bad... during start up or after it got to operating temperature?

[kahouna23]

If you ran the codes on the car, you'd probably get a P0420 code which generally means your cat has seen better days. The internal portion of your cat is probably one huge chunk of melted honeycomb crap. Go to your local exhaust shop and they'll normally do a test on the cat for free.

[v6guam]

Thanks guys...The car would run rough and rich after start up. The cat has been gutted for over a year.
The SES light would almost always come on while I decelerate. The light would come on and the engine seemed to smooth out a little. Now with the O2's unplugged the car runs great. No light no rich gas smell...I don't get it...

[v6guam]

any thing?

[94Redbird]

The reason I asked if you were having problems immediately after start up is because when you first start the car the O2 circuit is in open loop meaning they are not used... instead a default signal is sent to maintain a maximum efficiency until the engine gets to operating temperature or has been running for a few minutes. Once it reaches operating temperature the circuit goes into closed loop meaning the sensors take over and send the voltage signal. If a sensor malfunctions the computer will spit out a code and the circuit is supposed to go back to open loop and use the default signal. Sounds to me like for some reason it's not going to open loop and that's why it runs fine when you unplug the sensors... but bottom line it seems you need to replace one of them. To see which one is faulty either get the code scanned or measure the voltage on each sensor while the car is running. While cold it should be around 0.1V or 0.2V. When it warms up to operating temp (closed loop) it should fluctuate between 0.1V and 0.9V.