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Thread: advice please: part throttle power loss - no codes

  1. #1
    Join Date
    Nov 2010
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    Central, MO, USA
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    1993 BMW 850Ci

    advice please: part throttle power loss - no codes

    Hi. 1993 850Ci with manual transmission. Acceleration is perfect, but cruising at part throttle at any speed I will feel a sudden loss of power. Feels exactly like the engine drops to 6 cylinders. Pressing the throttle from that position confirms the loss of power, but releasing the throttle and then pressing it brings back full power. It feels like the throttle off position "resets" the computer.

    Testing the DK motors while stationary shows no problems - both respond properly and maintain part open positions.

    Most recent work was replacing both DMEs as well as new distributors/rotors. The EML unit has never been changed.

    Most perplexing to me: there are NO CODES.

    Has anyone seen this misbehavior before?

    Thanks!

    Mark in mid-MO
    1993 BMW 850Ci 6-speed
    2011 Cadi CTS coupe 6-speed

  2. #2
    Join Date
    Oct 2016
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    1991 850

    Cam Position Sensors

    Quote Originally Posted by ByMW View Post
    Hi. 1993 850Ci with manual transmission. Acceleration is perfect, but cruising at part throttle at any speed I will feel a sudden loss of power. Feels exactly like the engine drops to 6 cylinders. Pressing the throttle from that position confirms the loss of power, but releasing the throttle and then pressing it brings back full power. It feels like the throttle off position "resets" the computer.

    Testing the DK motors while stationary shows no problems - both respond properly and maintain part open positions.

    Most recent work was replacing both DMEs as well as new distributors/rotors. The EML unit has never been changed.

    Most perplexing to me: there are NO CODES.

    Has anyone seen this misbehavior before?

    Thanks!

    Cam Position Sensor (S) are bad. AKA Doughnut sensors. These are the ones that go to the 6 and 12 Sparkplug wires.

    Unplug from the front under the Oil Fill. Test with a Multimeter from the inside tab to the outside, one side should give you infinity, the other a reading. From Memory it should be less than 1 ohm. Shogun has posted factory spec before



    Crank Position Sensor AKA the other two should read 550 Ohms

  3. #3
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    Thank you, and I will test them; but have you seen these sensors fail with NO CODE set in the fault memory? I am doubtful because all the spark wires (including the CYL ID sensors) were replace with new OEM 6 months ago. I have seen the Cam position sensor fault many times over the years (usually due to ignition problems)... but it always set a code.

    Mark in mid-MO
    1993 BMW 850Ci 6-speed
    2011 Cadi CTS coupe 6-speed

  4. #4
    Join Date
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    93 850Ci, 09 Caddy SRX
    Quote Originally Posted by rjjablo View Post
    Cam Position Sensor (S) are bad. AKA Doughnut sensors. These are the ones that go to the 6 and 12 Sparkplug
    What he said.
    My ‘93 had the exact same issue after replacing old wires with OEM supplier wires…after many months of this it was suggested I replace with BMW OEM wires. That’s been at least 10yrs ago. No issues since.
    1993 850Ci.....16 years & 164,000 miles and counting!

  5. #5
    Join Date
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    1991 850

    This was critical

    Quote Originally Posted by ByMW View Post
    Thank you, and I will test them; but have you seen these sensors fail with NO CODE set in the fault memory? I am doubtful because all the spark wires (including the CYL ID sensors) were replace with new OEM 6 months ago. I have seen the Cam position sensor fault many times over the years (usually due to ignition problems)... but it always set a code.
    You did not say this initially and is very critical.

    I am looking at the same but I replaced my ID Sensor two years ago and now I get the Start for 3 second routine and before I spend more $ on new sensors I and you need to test them again and make sure the Resistance is correct.

    I also bought the OEM ones because of all the problems people had with the "Value" priced version

    Waiting for someone more knowledgeable to chime in as to the Longevity of these Sensors

    Also Check # 6 and #12 for continuity. I had problems for a while with #12 sparkplug boot not seating all the way and it would cut out but not the get back into the gas cut out solution

  6. #6
    Join Date
    Jun 2008
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    SF Bay Area
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    Supercharged 850ci
    Cyl position sensors will most definitely throw a code #16, if you don't have that code that is not your problem.
    Did this just start happening?
    Have your throttles been rebuilt already?

  7. #7
    Join Date
    Jul 2010
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    toronto,canada
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    1991 bmw 850i
    I can confirm that my 91 6spd had the same symptoms - cutout/low power under partial load, seems to reset if you let off gas then accelerate again, no codes. Passenger side donut was bad - replace and problem fixed (3 years ago -no reoccurrence)

  8. #8
    Join Date
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    Yes, this is a new symptom, but the car has been sitting all winter. I've put in fresh fuel, but it seems to be an electrical issue. Throttles have not been opened since I first got the car 12 years ago. I will check the cyl ID sensor resistances this weekend.
    Thank you, everyone, for your help.

    Mark in mid-MO
    1993 BMW 850Ci 6-speed
    2011 Cadi CTS coupe 6-speed

  9. #9
    Join Date
    May 2022
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    '93 E31; '00 E38 and E39

    E31 V12 Throttle Issue Solution?

    Quote Originally Posted by pollack137 View Post
    I can confirm that my 91 6spd had the same symptoms - cutout/low power under partial load, seems to reset if you let off gas then accelerate again, no codes. Passenger side donut was bad - replace and problem fixed (3 years ago -no reoccurrence)
    Hi there. I have the same issue with my 1993 6-speed. Can you explain what you mean by "passenger side donut?" Are you referencing the spark plug sensor? Did you change the full wire loom and isn.t a sensor suppose to throw a code #16 if an issue is detected? Thanks for whatever details you can supply!

  10. #10
    Join Date
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    My car had this exact symptom for over a year from the day I bought it. It did have code 16 but did not light the CEL. I replaced the donuts with genuine BMW parts and the car has never had an issue again. The word "donut" in this context refers to the same CID, spark sensor, ID sensor, pulse generator, etc etc.

  11. #11
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    Oh, and for what it's worth, in my experience the resistance testing on the donuts doesn't tell you much if anything. Both of my banks were symptomatic of dying or dead CIDs (losing 6 on cold starts, losing the other 6 at light/partial throttle, being able to reset by lifting the gas) and both banks tested within normal limits. After ruling out everything else I replaced both one at a time and found first I fixed the cold start dropout and then later fixed the part throttle drop out. So without any doubt the sensors were indeed the problem despite testing fine. It should be noted they appeared to be aftermarket units and they were different in appearance from each other so probably different manufacturers as well. As always, your mileage may vary.

  12. #12
    Join Date
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    Follow up...

    First of all - SINCERE APOLOGIES: there was no code on bank one, but bank two shows the expected "cylinder ID sensor" fault.

    But no "check engine light"... I still don't understand that.

    I tested the resistance of the donut sensor on #12 - every combination of two tabs shows circuit either full open or full closed. I think the sensor is faulty. I have ordered a replacement.

    Thanks to Shogun for posting pictures of the removal of the distributor end of the plug wire. I was able to remove #12 wire from the loom. It would be very difficult to remove the boot and right angle connector with the wire in the car. Lots of grease is the key. I am quite disappointed that the new Bremi wire set installed just six months ago should have a failure of the cylinder ID sensor!

    Hopefully next week I will have further follow-up with the repair completed.

    Hoping to take the car to a club event in early June!

    Thank you everyone who has responded. This forum makes ownership possible for me.

    Mark in mid-MO
    1993 BMW 850Ci 6-speed
    2011 Cadi CTS coupe 6-speed

  13. #13
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    Nope - no joy.

    The new pulse generator measured the same as the old - essentially zero resistance between pins one and two (which makes sense because it's just a coil of wire). I installed it and things were good for 25 miles. Then, on a hot day, it behaved exactly as before. Same code: bank 2: cylinder ID sensor.

    The resistance of #12 spark plug wire is 5.86 kOhm (it is labeled as 5 kOhm). The spark plug is the proper 1 kOhm plug. All of the ignition components are fresh (6 months old: DME, coil, distributor cap and rotor, all wires and spark plugs).

    I thought I had seen every example of this kind of failure, but this has me perplexed. Something is causing a low current condition on #12, but I can't identify it.

    I may try bypassing the OEM wire with a zero resistance plug wire and see if the ID sensor is happier. Don't know what else to try.

    Thanks for your thoughts.

    Mark in mid-MO
    1993 BMW 850Ci 6-speed
    2011 Cadi CTS coupe 6-speed

  14. #14
    Join Date
    Oct 2016
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    1991 850

    Swap Coils

    Coils can have heat related problems. Swap them and see if problem moves

    Same with your new cam position Sensor Swap them and see if problem moves

    Fuel Pump Relays, Swap them or test them. They will cause a side to stop running, Mine would hit a bump and voila 6 cylinders

  15. #15
    Join Date
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    '93 E31; '00 E38 and E39
    Quick update: Thanks to the comments from rjjablo, pollack137 and LappingLuke, we went ahead and changed the ignition wiring looms (with the built in cam sensors) at both sides, part numbers 12121733007 and 12121733010, as well as all 12 plugs (NGK 2288 BKR6EK) and the 1993 850Ci is up and running again perfectly!

  16. #16
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    Great!

  17. #17
    Join Date
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    Quote Originally Posted by rjjablo View Post
    Coils can have heat related problems. Swap them and see if problem moves
    This is good advice. However, since these coils are only 6 months old (as are all the ignition components), I'm just going to replace them with an after-market solution. All of the other parts of the spark chain are working properly, so I'm going to try increasing the voltage in the plug wire. I'll let you know how it goes. Thanks!

    Mark in mid-MO
    1993 BMW 850Ci 6-speed
    2011 Cadi CTS coupe 6-speed

  18. #18
    Join Date
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    1993 BMW 850Ci
    I hope this will be my last update (fingers crossed).

    I installed the MSD 8207 coils and the car is running normally again. No problems after three days and 30 miles in varying conditions.

    Was the 6 month old Bosch coil from Slovenia defective? Possibly. Would I put another in my car and risk being here again in 6 months? No. Does the extra voltage confer any performance gain? No. But it reliably triggers the Cylinder ID sensor.

    For anyone making this change: you have to swap out the coil end connector on the coil wire for the one supplied in the kit, which is not difficult. You have to fabricate an adapter bracket to mount it in the car - again, not difficult. The stock plug wires are fine. The MSD primary has a + and - terminal. On my car the two primary wires from the DME are both black; they attach to an 8mm terminal and a 10mm terminal on the OEM coil. Pictures of old Bosch coils show the 8mm post labeled "1" and the 10mm post labeled "15" - which makes the smaller one negative and the larger one positive. That's how I connected mine and they work fine.

    Thanks again, for the support from this community. There are lots of past threads about the "MSD SS Blaster" coils on M70 engines.

    Mark in mid-MO
    1993 BMW 850Ci 6-speed
    2011 Cadi CTS coupe 6-speed

  19. #19
    Join Date
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    93 850Ci, 09 Caddy SRX
    Excellent! Glad you got it sorted. Maybe I’ll do this mod so day. Years ago someone here was selling brackets for the MSD coils.
    1993 850Ci.....16 years & 164,000 miles and counting!

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