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Thread: Limp Mode Issues (1991 850i w/ 4 HP-24)

  1. #1
    Join Date
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    Limp Mode Issues (1991 850i w/ 4 HP-24)

    Situation: I have a 91 850 that is dropping into limp mode under normal acceleration. I have a few errors:

    3F: Torque Converter Clutch
    49: Vehicle Speed not Present

    Sometimes these will pop up:
    29: Air Flow Sensor
    C9: Emission (Lambda) control

    I can pull over, shut the car down, start it up and be off again, but as soon as I accelerate moderately, it drops into limp. If i'm up to speed and get on it, I get the audible "ding" in the cockpit (which tells me I just threw the code), but it continues to drive until I come to a stop... Then it's snails pace until I shut it down and fire it back up again.

    What I have done:
    A. Swapped plug wires, rotors, caps. Now now I have both banks firing. Initially, I had 1-6 failing all the time.
    B. Cleared codes
    C. Hard Reset
    D. Cleaned the Rear Diff Speed Sensor

    Currently Executing:
    I. Changing the fluid filter now. (There is normal debris on the magnets. It was actually pretty clean)
    II. Placing an order for a new Driveshaft Speed Sensor (Inside transmission)

    Questions:
    1. What should the resistance on the Driveshaft speed sensor be? Mine is 328.3.
    2. What else should I check that could be leading to my limp mode situation.
    3. Could C9 and 29 cascade me into limp mode? (I'm leaning towards this, but replacing the CSS is a *lot* less expensive than replacing a MAF....that's why i'm replacing the CSS first.)
    Last edited by Cup1d; 05-09-2018 at 03:20 PM.

  2. #2
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    There are 2 CPS, they should be reading 0.5k ohm between pins 1 and 2 -+ 10%.
    If you are reading 0.328 it is bad.
    You need to replace MAF as yours is failing and both o2 sensors.
    Then see if LHM is still present.

  3. #3
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    I'm sorry, I completely screwed up. I mean *Driveshaft Speed Sensor*. This guy is inside the transmission. I believe it to be triggering the code. The engine is running fine.

    The Caps, Wires, Rotors, and O2 sensors are all new.

  4. #4
    Join Date
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    Santa Barbara
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    91 Dinan860 & 91 850 6sp
    more likely than not, the "Trans Fail Safe" or "Limp" mode is being triggered by an engine fault, NOT anything to do with the transmission, speed sensor, or whathaveyou. That's a secondary code.

    Don't be so quick to assume "the engine is running fine", because it isn't.
    '91 Dinan 860 Stage III (new 6L engine)
    '91 Dinan 850 TT stage III (brand new engine) 21st Century Tech meets 18th Century Dinan...
    '91 850i 6sp (mint) (sold)
    '90 Dinan 750iL TT stage III (Guido - The Beast)
    '94 850 CSi The Detroit Auto Show car (restored to factory perfect) (sold)
    '96 850Ci, The George Carlin car
    ''73 3.0 csi, '08 535i, '03 X5 4.6is
    ...and a few other non BMW cars

  5. #5
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    Do you have a suggestion?

    Quote Originally Posted by cartoonz View Post
    more likely than not, the "Trans Fail Safe" or "Limp" mode is being triggered by an engine fault, NOT anything to do with the transmission, speed sensor, or whathaveyou. That's a secondary code.

    Don't be so quick to assume "the engine is running fine", because it isn't.

  6. #6
    Join Date
    May 2013
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    1993 BMW 850CI
    Have you ever cleaned your DK's (Throttle bodies)? What spark plugs are you running? If you are running modern plugs with 5k ohm resistors that can be problematic, try NGK BKR6EK dual ground 1000 ohm resistor plugs in cylinders 6 and 12 to see if that resolves the problem. If your throttle body armatures and brushes are all gunked up, this can also lead to these sorts of Limp problems. I know this from having the same problems you are having, and these issues now fixed, and no more problems.

  7. #7
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    Thank you, sir! This was incredibly helpful. I'll pull one of the plugs to determine what the owner has installed. If it is not these, I'll try your recommendation as well. After that, I'll inspect the DKs!

    Thanks again everybody!

    Quote Originally Posted by Mikekugel View Post
    Have you ever cleaned your DK's (Throttle bodies)? What spark plugs are you running? If you are running modern plugs with 5k ohm resistors that can be problematic, try NGK BKR6EK dual ground 1000 ohm resistor plugs in cylinders 6 and 12 to see if that resolves the problem. If your throttle body armatures and brushes are all gunked up, this can also lead to these sorts of Limp problems. I know this from having the same problems you are having, and these issues now fixed, and no more problems.
    Last edited by Cup1d; 05-09-2018 at 06:19 PM.

  8. #8
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    49: Vehicle Speed not Present
    Is that from a Peake tester? Did you check the speed sensor on the final drive? http://www.bmwe34.net/E34main/Mainte...eed_sensor.htm
    Shogun tricks and tips for the E32 series are HERE!

  9. #9
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    Yes sir! I'm using the Peake.

    I pulled the one out of the rear diff yesterday. It certainly had gunk on it so I cleaned it and popped it back for a test to no avail.

    Quote Originally Posted by shogun View Post
    49: Vehicle Speed not Present
    Is that from a Peake tester? Did you check the speed sensor on the final drive? http://www.bmwe34.net/E34main/Mainte...eed_sensor.htm

  10. #10
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    Quote Originally Posted by Cup1d View Post
    Do you have a suggestion?
    This: You need to replace MAF as yours is failing and both o2 sensors.
    And check spark plugs.

  11. #11
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    91 850i, 01 740i, 06 760
    I had very similar problem with my 91 850i. Was intermittent at first doing just like you describe. Then when it completely failed the car would not shift out of 1st gear (because transmission controller doesnt know car is moving).

    Output speed sensor in the transmission was open circuit. Drop the pan and its right there... easy fix. You can ohm it out from the transmission connector.

    http://km5tz.com/BMW%20850iP8.htm

    Read your post again and looks like resistance of your speed sensor is OK so maybe something else but easily replaced...
    Last edited by BMSman; 05-09-2018 at 11:24 PM.

  12. #12
    Join Date
    Nov 2014
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    Vena, Sweden
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    1992 BMW 850ia
    The first error you listed, 3F: Torque Converter Clutch, says to me that the ATF level is low. When accelerating the level gets even lower which will cause the limp mode. The other errors can be a result of the engine being in limp mode. My car behaved like this when I bought it some years ago when I did not know anything about the E31 and its various sensors and computers.
    Last edited by peake; 05-10-2018 at 10:03 AM.

  13. #13
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    Thanks for all the responses! I'm finding out more and more that *everything* is an adventure with E31s... I plan to methodically go through it when I get off work today.

  14. #14
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    are slow
    Unplug one MAF (remember, the intake tube on the right side is for the left bank's manifold and vice versa) and see which side runs like crap.

    Lambda codes tend get thrown because of vacuum leaks/false air, so I'd start with the maf.
    Last edited by XAlt; 05-10-2018 at 01:56 PM.

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