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  1. #1
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    Member No: 21136 markmalin is an unknown quantity at this point markmalin's Avatar
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    Intermittent cut-out problems. Help.

    Hi guys,

    This is a tough one. I just bought an '88 535i 5-speed and it has these intermittent problems that I'm about pulling my hair out over. I listed the issues below, along with what I've tried so far. I've tried to be methodical. If anyone is willing, please read this through and offer some suggestions. Also, if you will, notice what I've already done before suggesting ideas. I think I've hit most of the biggies. I need some methodical way of debugging this rather than a "replac the _____ I did this and mine worked" approach, if you know what I mean. Thanks a bunch, everyone!

    Problem(s):

    Engine cuts out intermittently – When it does this, there is an immediate, sudden drop in engine power (the car bucks), the MPG gauge on the dash swings to the far left and sometimes the tack jumps to the left. This happens randomly, sometimes as few as 5 times a day, but most often within the first 20 minutes of running the car. It lasts about Ό second then the car runs normally. It can happen any time during the day. When it's doing this, I can feel the Fuel Pump relay clicking if I put my fingers on it. So it's like the ECU is telling the thing to drop out.

    Along with this, when the car is started from dead cold in the morning, it runs fine (except for a few cut-outs described above), then at about 4 minutes 20 seconds the car begins misfiring badly and loosing power. After about 1-2 minutes of this it evens out and is fine for the rest of the day. Note: After exhibiting the problem in the morning, the car will often run fine the rest of the day even after sitting 9 hours on a work day. I talked with the previous owner and confirmed it’s been doing this for years. (This seems to not be moisture related because I drove home from work after the car sat in the pouring rain all day and never had a problem.)

    When running normally, I think the car is running rich, but other than that the engine is smooth and quiet and has good power. Revs up nicely, sounds solid and smooth. When it runs, it runs very nicely.

    What I’ve tried with no effect to the problems:

    - bypassed the main relay with jumper.
    - bypassed fuel pump relay with jumper.
    - run with O2 sensor unplugged.
    - run with Throttle Position Sensor disconnected.
    - bypassed CODE relay (in OBC relay box).
    - cleaned and re-seated every connector on the fuel injection wire harness (inside engine bay and under dash near ECU).
    - cleaned every ground connection in engine bay and under dash (not in trunk, though) and applied contact cleaner, then electrical grease.
    - wiggled every wire I could find under the dash, wiggled every wire and connector I could find under the hood.

    Parts replaced or tried with no effect:

    - crank position sensor and speed sensor on the flywheel – new
    - fuel filter - new
    - fuel pump relay – new
    - coolant temp sensor – new
    - spark plugs - new
    - plug wires, rotor and cap - new
    - thermo time switch – swapped with used
    - Air Flow Meter – swapped with used
    - Motronic unit – swapped with used
    - Vacuum hoses (small ones) – new
    - Intake boot – replaced with known good used
    - Ignition coil – previous owner swapped with used

    I thought next I'd try ohming out the fuel injection wire harness. The other thing would be to bypass both the Fuel Pump and Main relays. I've bypassed each individually so I know it's not the relays OR control to the relays that's causing these issues. Other more "shot-gun" things are to swap the ICV, sap instrument cluster and a different AFM.

    As an asside -- does anyone have a known good fuel injection wire harness they'd sell REALLy cheap? Or maybe let me try out, or be willing to trade for something?

    Thanks!
    Mark.
    <br><br>
    Mark - in Madison, WI
    '85 635csi 5-speed
    '03 525iA
    <br><br>

    <br><br>
    Che bella macchina!


  2. #2
    TJ
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    that's a tough one

    have you tried jiggling the key in the ignition to see if that causes it to cut out?

  3. #3
    Ray7er6ers5er3er
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    1st off when U buy a 'new' car you have to assume

    the maintenance has been neglected no matter what the owner says, unless you know him or he's got reciepts. That said, you may be on the right track as to the ECU getting wrong info. The ECU temp sensor is brand new and light blue right?, but are you certain the connection is good. Clean and strip back the wire a few inches. I would then remove the ECU and resolder the 6 solder points that fail at about this age. Don't just reflow, but add atouch of solder as well. I have the same car as you, and it's the best running, easiest car to maintain I've ever had...once I caught up on the maintenance that is. When swapping out a major part(AFM, ECU) be dam sure it's a GOOD one. Many headaches have been caused by using a so so used part...misleading you to look in the wrong directions and wasting a ton of time and money. Ask me how I know.DUh
    If it were my car I would also change the sweep on the AFM board (see archives or e-mail me) ater 20 years they've done they're job.
    PS plug the o2 sensor back in or replace it. My 02

  4. #4
    Ray7er6ers5er3er
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    PS how is the battery and it's cnnections?


  5. #5
    aussiebastard
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    Re: Intermittent cut-out problems. Help.

    i agree with Ray about the ECU - I have had 3 used replacements in the recent past hat each had its own problem - intermittent non-start, no idle, misfire & high emissions - I'd try another ECU - maybe a "known good" one - I finally got a good one and life is good

  6. #6
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    Re: Intermittent cut-out problems. Help.

    Sorry I was not around back when you posted this. Your AIR BOX a.k.a Mass air flow sensor is kaput. Replace with known good one. Or a rebuilt.

  7. #7
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    Check these connections

    After I changed my distributor cap and rotor, I took the car out for a test. It ran perfect for about 30 minutes. Then slowing for a stop light, the engine quit. No warning, nothing. Started with no problem. Continued to the house and it happened again. Quit in a right hand turn, no power steering, I had my hands full. Let it sit overnight. Next day, after about 5 minutes, one cylinder missed. Happened again about 5 minutes later. Then later the engine quit again. Nothing. Started immediately. The problem was one retaining clip that holds the ignition wires to the plugs and distributor had detached when I put on the new parts. I lost the clip trying to put it on. I thought it was no big deal. I had a spared ignition wire with the clip. It fixed the problem. Make sure all your ignition wires have the retaining clips!

  8. #8
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    Member No: 51648 TamsDaMan is an unknown quantity at this point TamsDaMan's Avatar
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    No Science Behind This... But

    Ignition Switch

    If there is an intermittent connection at the key that causes power to be interrupted to "ignition" which is an input to the ECU, then that could cause sudden lack of ignition problems and quickly recover when ignition is restored since the engine has momentum. An idea.

  9. #9
    mrmojorisin
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    Re: that's a tough one

    do you use just the ignition key or do you have a whole keyring full of keys hanging from the ignition?

  10. #10
    mitch in Oregon
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    Re: Intermittent cut-out problems. Help.

    Had intermittment no start condition, ended up being caused by an bad Main Relay. The relay contacts were cooked and would only make intermittment connection.

    Easy test. Took a short length of heavy sized wire and soldered male solderless connections on each end. Unplug the Main Relay and jumper the power terminals (see diagram printed on the body of the main relay). Drive and see if the cutout goes away.

    Quick and easy test.

    Best of luck,

    Mitch

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