I replaced my O2 sensor a couple of weeks ago. At the time, it was throwing code 21 (Oxygen Sensor Circuit) and 51 (Oxygen Sensor, Lean condition). Before I changed it, I cleared the codes a few times and would alternate between 51 (lean) and 52 (rich), but always got 21.
Replaced the O2 sensor and now I'm getting 52, running rich. I've cleared the code twice and still it only gives me 12, 52, and 55.
Back story... Before all of this, the Jeep was running fine. I started to replace the O2 sensor as a precautionary tune-up in November, because I've had the Jeep for six years and never replaced it and wasn't sure if/when it was last changed by the PO's. It was seized and I couldn't get it out, even after a LOT of PB blaster and elbow grease. After all of that, and disconnecting it a few times, it eventually led to error codes 21 and 51, which I figured is from the overuse of PB blaster that eventually put the nail in the coffin for the sensor. Ended up taking it to a shop and had them remove it and install the new sensor that I had already bought.
Is there something I should check with the O2 sensor to ensure it's working? Put a meter on it? Is there something else I should check? I'm at a loss.
It does start. After I reset the codes, the first start-up, it's fine (I'm in NY and it's been very cold the last few mornings). After the first or second startup, it would run like it's hesitating. A lot of smelly exhaust. But after it warms up, it seems to idle fine. If I start it up and try to step on the accelerator before it warms up, it sounds like it's wanting to stall - I'm guessing that it's getting way too much gas and choking.
Humor me here for a minute. You are reading rich in the exhaust not lean which means you are getting too much fuel into the system. The problem is fuel related because the sensor is reading correctly. Get yourself a fuel guage and read the fuel pressure. You might have a bad regulator, pinched fuel line, or a bad injector. Fuel pressure test is my .02
The OP says that he was running fine but getting a few codes before his attempt to remove the O2 sensor. He could not get the O2 sensor out so he had a local mechanic replace it for him.
Why does he get one good cold start up after dumping the learned memory?
Would high fuel pressure cause this run rich condition? Would a pinched return fuel line do so?
What makes me think that either the brain is sending too much fuel to this engine for the air it is getting.
Could it be retarded timing? Bad IAC?
What I get stuck on is why does he get one good cold start after dumping the memory?