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Running lean

Discussion in 'Troubleshooting' started by Jabber88, Dec 6, 2016.

  1. Hey everyone,

    So I recently took my car to BMW for a new o2 sensor. Since then my AFR's have been nothing but lean. Everytime I get near the gas sometimes even just idling I've seen 20:1 but the car has no symptoms and if it wasn't for my jb4 I wouldn't even know. I been waiting for it to throw a code but it's been two weeks now and nothing. The car targets boosts and holds boost fine with no codes even after racing and beating another tuned 335i which I didnt expect.

    I did take the car back to BMW and asked them check the car. They said everything was ok but I could use a walnut blast which they were only going to charge me $1000 for lol. I obviously declined that paid my 220 for diagnostics and left a little discouraged.

    Anyone have any ideas what this could be besides oxygen sensors and is there anyway to test O2 sensors?
    Last edited: Dec 6, 2016
  2. Icewall

    Icewall Lurker

    just replace the o2 sensors. very common. my car would hit 20:1 on the jb4 readout. I could get it out of that state and it was fine for months. eventually both o2 sensors failed and it threw codes.
  3. Thanks for the input. I'm hoping it's just the O2 sensor. I've been waiting to put on my dp and fmic until I got this figured out.

    Is there anyway to test the O2 sensors?
  4. BrettJP

    BrettJP Private

    08 335xi e92
    I know this is really late, but...

    You can test O2 sensors with a multimeter. The idea behind these kinds of sensors is simple, the more oxygen in the sampled air, the more the sensor will conduct electricity. I don't remember the exact numbers, but if you read something stupid low or even zero, or something stupid high, the sensor is almost surely bad. But at the same time of course, the sensor could indicate a problem somewhere else like a vacuum leak, so make sure to do your due diligence in investigating possible related issues.
  5. Chris

    Chris New Member

    2010 135i
    Try to reset the lambda adaptations and see what happens from there