02 sensor issues

Hello,

By disconnecting the O2 sensor the engine management system (ECM) will substitute the O2 value with a pre-programmed value.

The most likely reason that your engine is running rich with the O2 sensor connected is that the O2 sensor is detecting a lean running condition and the ECM is trying to correct this by adding fuel.

A lean running condition can be caused by an intake system air leak, vacuum leak, exhaust leak or even by an aftermarket induction system.

Here is a guide on how to check for a lean condition:

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Please let us know how you get along

Cheers, Boris

Don't forget a spark-related misfire. Unburned fuel will be smelled at the tail pipe, but it's the unburned oxygen that will be detected by the O2 sensor.

Happy Friday to you guys.