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Thread: Help With a Weird O2 Sensor Issue

  1. #1
    Join Date
    Feb 2015
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    Kuna, Idaho
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    Question Help With a Weird O2 Sensor Issue

    A little background. 1991 850i. Have been working on it for 4 years on and off. A buddy of mine, who is the lead tech at the local BMW dealer (fellow BMWCCA member), has recently been helping me figure this thing out. He discovered a broken wire in the harness that the 1-6 crankshaft position sensor plugs into which kept the 1-6 fuel pump from running. That is now fixed. Now there is another weird issue that I'm asking about because we are both (kind of) stumped. He is super well versed on all the newer BMW's, as well as E30's as he has 2 of them, but our "in between" cars may be giving him some crap.

    The car runs great, it does idle a bit weird. You definitely can't stand a nickle on edge on the engine without it falling over! When running the codes (GT1V44), we're getting a 201 O2 sensor issue (too lean) bank 1-6. No issues or faults on bank 7-12. He discovered that the O2 sensor is not switching. We have tried 2 other O2 sensors and they do not switch either. The one on bank 7-12 switches fine, but not 1-6. So here's the question.

    Is the "switching" of the O2 sensors strictly a function of the O2 sensor itself, or is there some other "thing" that adds information that tells the O2 sensor to switch or not? Not even sure how or what to ask here. The car is so close to being drivable, that this one thing is making us both crazy. He's leaning toward a vacuum leak. His thinking is (if I can reiterate it correctly), that there is so much air blowing through the system, that the O2 sensor can't switch in order to get the DME to add all the fuel it can to compensate for the lean condition. I however, have no clue.

    If anyone can shed light on this, both of us would really appreciate it. In a couple of weeks, on a Saturday, we'll be bringing it into the dealer and using their "big gun" smoke machine to either find or eliminate a vacuum leak as the cause, but if there are any other theories/suggestions/ideas or whatever, I would love to hear them. The thought of pulling the intakes (again) makes me wanna jump off a cliff without a parachute...

    Thanks,

    Mike
    Mike Drives:
    BMW's
    E24 - 635CSiA - (1) 1985 (US)
    E24 - 635CSi - (1) 1985 (EC)
    E31 - 850iA - (1) 1991 (Black)
    E31 - 850iA - (1) 1991 (Calypso Red)

    E32 - 740iA - (1) 1994
    E32 - 750iA - (1) 1990 (Not an "L") (EC German National)
    E32 - 735iL - (2) 1990
    E32 - 750iL - (1) 1990

    E38 - 740iLA - (2) (1) 1997 & (1) 1998
    E38 - 750iLA - (1) 1998
    E38 - 740iA - (1) 2000 "Short Sport"
    E39 - 528iA - (2) - 2000 & (1) 1997
    Also:
    2015 Ram 3500 Dually, Cumins 6.7, Std.Cab. Long box 4x4 (To haul all this junk when necessary)
    2014 Dodge Dart Rallye (Daily Driver)
    2007 Mercedes Benz CL600 (Brabus SV12S)
    Mercedes Benz SL's - (1) (2002) & (1) 1999 500 - (1) 1999 600
    1967 Buick Riviera (2)

  2. #2
    Join Date
    May 2009
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    If it's old CAT in car time to replace it or go straight pipe. That sound like my issues
    At ideal something wasnt right turn out to be broken stuff inside cat.

    Sent from my SM-G960F using Tapatalk

    F13platform, on Flickr

  3. #3
    Join Date
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    The O2 sensor does not do any switching - it responds to changes in air/fuel mixture.

    When the engine is at operating temperature the Lambda sensor is informing the ECU of the remaining Oxygen level in the exhaust - and that, in turn, indicates the initial air/fuel mixture. The M70/M60/M62/M62TUB engines employ narrow band Lambda sensors which mean they can only indicate a mixture is too weak or too lean. The ECU continually makes small adjustments to the injector dwell in response to the raw Lambda output - for example, the Lambda will report that the mixture is too weak and the ECU will increase injector dwell (the time it is open) - it does this in tiny increments - until the Lambda signal ‘flops’ high indicating that the mixture is too rich.

    This seems a strange system, but the early Lambda sensors available were narrow band and all engine ECU's controlled the mixture by continually adjusting the fuel/air mixture so that the output from the sensor continually flops around.

    So, your problem is a lean mixture that cannot be adjusted out by adaptations - much more information regarding fuel/air mixture here:

    https://www.meeknet.co.uk/E38/Diagnostics.htm
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  4. #4
    Join Date
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    f13platform: The cats were deleted before I purchased the car. In fact, there is literally nothing past the resonator. I need to get serious about mufflers.

    Timm: Thanks for the pointer and the link. I will read up and try to determine what's going on.

    Thank you both. I'll be back!

    Mike
    Mike Drives:
    BMW's
    E24 - 635CSiA - (1) 1985 (US)
    E24 - 635CSi - (1) 1985 (EC)
    E31 - 850iA - (1) 1991 (Black)
    E31 - 850iA - (1) 1991 (Calypso Red)

    E32 - 740iA - (1) 1994
    E32 - 750iA - (1) 1990 (Not an "L") (EC German National)
    E32 - 735iL - (2) 1990
    E32 - 750iL - (1) 1990

    E38 - 740iLA - (2) (1) 1997 & (1) 1998
    E38 - 750iLA - (1) 1998
    E38 - 740iA - (1) 2000 "Short Sport"
    E39 - 528iA - (2) - 2000 & (1) 1997
    Also:
    2015 Ram 3500 Dually, Cumins 6.7, Std.Cab. Long box 4x4 (To haul all this junk when necessary)
    2014 Dodge Dart Rallye (Daily Driver)
    2007 Mercedes Benz CL600 (Brabus SV12S)
    Mercedes Benz SL's - (1) (2002) & (1) 1999 500 - (1) 1999 600
    1967 Buick Riviera (2)

  5. #5
    Join Date
    Feb 2015
    Location
    Kuna, Idaho
    Posts
    736
    My Cars
    Too Many Cars (NOT!)
    Update;

    The BMW tech and I took the car over to the dealer on Saturday, smoke tested the crap out of it, and discovered a bunch of vacuum leaks!

    Grrrrrrrrrrrrr!

    Thank you to all who helped. Much appreciated.

    Mike
    Mike Drives:
    BMW's
    E24 - 635CSiA - (1) 1985 (US)
    E24 - 635CSi - (1) 1985 (EC)
    E31 - 850iA - (1) 1991 (Black)
    E31 - 850iA - (1) 1991 (Calypso Red)

    E32 - 740iA - (1) 1994
    E32 - 750iA - (1) 1990 (Not an "L") (EC German National)
    E32 - 735iL - (2) 1990
    E32 - 750iL - (1) 1990

    E38 - 740iLA - (2) (1) 1997 & (1) 1998
    E38 - 750iLA - (1) 1998
    E38 - 740iA - (1) 2000 "Short Sport"
    E39 - 528iA - (2) - 2000 & (1) 1997
    Also:
    2015 Ram 3500 Dually, Cumins 6.7, Std.Cab. Long box 4x4 (To haul all this junk when necessary)
    2014 Dodge Dart Rallye (Daily Driver)
    2007 Mercedes Benz CL600 (Brabus SV12S)
    Mercedes Benz SL's - (1) (2002) & (1) 1999 500 - (1) 1999 600
    1967 Buick Riviera (2)

  6. #6
    Join Date
    Dec 2013
    Location
    San Antonio
    Posts
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    850,76 2002 &530,84 633
    I would imagine the intake manifold gaskets are leaking and will need to be sealed up with some Reinzosil rtv sealant. This was the first thing I decided to do before I even thought about starting up the car I bought, but, mission creep set in and I ended up replacing most everything in fuel system, belts, tensioners, CIS and crank sensors, etc. And, if you remove the manifold, you might consider removing valve covers and tightening the banjo bolts and replacing the gaskets. Oh, while you have the covers off you could check the cam timing too!

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