[n54Newb]

hey there i bought a n54 and i changed the turbos i have been driving for 7000 miles since and now today when i was about to reverse park. i seen a small cloud of smoke. the smoke is grey-whitish not blue. it smells chemically. when i bought the car it came with catless dps but still has stock exhaust and secondary cats this car was already running without the secondary o2s sensors. i was told "mhd will code it out when you tune it".. the car doesnt limp or idle rough. how important are the secondary o2s and can they cause smoke if inactive?

[drymite]

Possibly i read mixed replys about cars not needing the secondary o2s and that it just monitors the cats and i also read that you need the secondary O2s because the n54 uses it for STFT-LTFT.

[n54Newb]

so does it cause smoke if im missing the secondary's?

[dmckmc]

Originally Posted by n54Newb

how important are the secondary o2s and can they cause smoke if inactive?

Smoking is most likely from valve seals, turbos, worn piston rings, pcv system, etc. secondary o2s monitor the efficiency of the primary cats.

[CarAbuser]

Secondary O2s are used to calibrate the primaries. Having them missing just means your afr readings will be incorrect and the car will start to drift lean or rich, so you'll lose power and eventually get a rough running engine.

[roadkillrob]

Originally Posted by CarAbuser

Secondary O2s are used to calibrate the primaries. Having them missing just means your afr readings will be incorrect and the car will start to drift lean or rich, so you'll lose power and eventually get a rough running engine.

This is spot on and even though tunes code them out, they don't code out them being active, the just suppress the error codes for catalyst inefficiency, but the secondaries still play a valuable role and continue to work even without cat's.