Start car... O2 sensor warms up and works fine.


Roughly 20-40 minutes pass, O2 sensor suddenly drops to .18-.20 volts and stays there. causes computer to push a bunch of extra fuel in.. of course.. but O2 sensor stays lean the whole time.


Shut car off, walk away for 30-40 minutes... come back..
O2 sensor works again.


Its a 3-wire, heated, been working fine for 6,000 miles... till now.

 

Just a WAG, but is there possibly a connector that is routed close to the exhaust or something else that may be heating it?

 

Is this the same O2 that was acting up like two months ago, or is this a new one?

 

A new one. the old one was doing other weird crap, like shutting itself off for no reason.

This one also never goes past .75 volts. usually they swing from 0V to 1.0V but this one only swings to .75 if its REALLY rich then back to 0V. It seems a random thing when it dies off too...

i have a valve cover leaking oil down the back of the motor. the connector gets soaked with oil occasionally... i wonder if that might be screwing it up?

 

The oil leak can do it. O2 sensors need outside air to function properly. It compares the outside air to the exhaust to tell how lean/rich the mixture is (ie how much voltage to send to the computer). If the oil runs down the wires into the sensor, it will block of the supply of fresh air. If this is the case, the sensor might need to be replaced again. To be sure, stop the oil leak and see what happens.

 

i would be suspicious of a wiring problem. ive had a wire going to a sensor that intermittently started acting up only when the engine is hot. tough to track them down sometimes but what i did was hookup the scanner and have someone giggle the wires at various engine temps till i found the frayed spot in the wiring, then replaced the bad wire.