Last week, my friend's turbo DelSol started reading lean on his air/fuel gauge, but the car was rich. We concluded it was is 02 sensor, so I swapped him my secondary o2 sensor for his "lean reading" 02 sensor, and whadda ya know, his is running good again, and mine was doing okay as well. So...

I thought I'd push my luck a little....

I went to get a downpipe welded up yesterday, and I remembered that I have an 02 sensor that reads progressively lean. If the primary o2 sensor is working correctly and the secondary 02 sensor (usually behind the cat) is reading lean, the ECU will think there is a cat and it is functioning correctly.

For time's sake, I now have a 2.5" downpipe straight back to my Greddy PE 2.5"... umm, "CATBACK" with one bend in the process. I have put over 50 miles on the car and... no CEL.

Now, the question: How could you duplicate this "lean reading" 02 sensor, or did I just luck up? Thanks!

 

maybe its old and dirty.