Quote:
Originally Posted by Darkrune
I put defoulers on BOTH of my O2 sensors during the install, thinking that it would be better to control engine check issues... ...When I took the defouler off the first O2 sensor and placed it directly into the exhaust stream, all of my issues went away....
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Modern cars use the upstream O2 sensor for closed loop running. If it wasn't in the exhaust stream, the engine is trying to operate in closed loop (running with feedback from the primary O2 sensor) with the sensor not reading that's actually going on, hence the issue.
The downstream, secondary O2 sensor is used for verifying catalyst efficiency. That's the one to put a defowler/O2sim on.
It's possible, however, that you've come across the underlying cause by replicating the symptoms. If the O2 sensors are iffy, get damaged, or are particularly sensitive to burned oil, they could be sending bad information to the ECU, hence the problems and catastrophic failure.