[syntax]

My friends 08 335xi bone stock and untuned does have a bank 2 precat (bank 2 sensor 1) code but im not sure if this is the reason his AFR on bank 2 is always 30. The car from a complete cold start instantly has an AFR of 30 on bank 2. I also noticed his STFT's on Bank 2 are always at 0 and never change, signaling O2 sensor issue, but I thought these cars stay open loop with AFRs until the O2s heat up which is roughly 30 seconds after a cold start before they rely on O2's for calculating AFR's. Last week i changed his cylinder 4 injector because of a misfire code which has returned and his valve cover gasket and plugs were also changed. He does have the same coils though. Can a precat o2 sensor cause a locked AFR at 30 (Holy shit) from a dead cold start? His AFR is always 30 whether he drives, at different speeds, or is idling or does a cold start. Im guessing O2 sensor or stuck injector, but I doubt its an injector because he said it didnt misfire bad on the cold start. The events are contradicting here between the way stuck injectors usually misfire from excess fuel and how these cars wait to heat up for O2 AFRs. Here is a log.

Log Info: Log begins right before car is started. Log lasts roughly 60 seconds only idling. Car hasnt been started in a week, temps are 32 degrees F outside (freezing point).
https://datazap.me/u/loganslow/cold-...og=0&data=3-21

[mweisdorfer]

Originally Posted by syntax

My friends 08 335xi bone stock and untuned does have a bank 2 precat (bank 2 sensor 1) code but im not sure if this is the reason his AFR on bank 2 is always 30. The car from a complete cold start instantly has an AFR of 30 on bank 2. I also noticed his STFT's on Bank 2 are always at 0 and never change, signaling O2 sensor issue, but I thought these cars stay open loop with AFRs until the O2s heat up which is roughly 30 seconds after a cold start before they rely on O2's for calculating AFR's. Last week i changed his cylinder 4 injector because of a misfire code which has returned and his valve cover gasket and plugs were also changed. He does have the same coils though. Can a precat o2 sensor cause a locked AFR at 30 (Holy shit) from a dead cold start? His AFR is always 30 whether he drives, at different speeds, or is idling or does a cold start. Im guessing O2 sensor or stuck injector, but I doubt its an injector because he said it didnt misfire bad on the cold start. The events are contradicting here between the way stuck injectors usually misfire from excess fuel and how these cars wait to heat up for O2 AFRs. Here is a log.

Log Info: Log begins right before car is started. Log lasts roughly 60 seconds only idling. Car hasnt been started in a week, temps are 32 degrees F outside (freezing point).
https://datazap.me/u/loganslow/cold-...&data=3-21

AFR should never go over 15.

Did you use INPA so see what the voltage looked like on the pre & post cat O2 sensors?

[langsbr]

My car did this same thing. I thought it was a bad o2 sensor as mine would read fine for a while, then go to 30:1.

Do you know the history of the car? you said untuned and unmodded - but had it ever been modded before?

After many frustrating steps troubleshooting, I found that one of the pins on the DME was pushed in slightly - enough to not make permanent connectivity to one of the O2 sensor pins. I was able to pull that pin out with some needle nose pliers and haven't had an issue since.

If everything checks out wiring wise, I'd suspect just a bad/dead/old sensor.