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Thread: 540i losing cylinders 1-4

  1. #1
    Join Date
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    540i losing cylinders 1-4

    Yesterday after a 25-30 minute drive in the city I was cruising home and cylinders 1-4 we're showing full lean (18:1 or higher)

    I admittedly didn't notice it until I was stopped at a light and noticed the shaking and poor acceleration.

    In the morning cold start revealed normal function (at least normal considering I have a couple of known vacuum leaks that o2 seems to handle well enough under closed loop)


    Tonight the same thing happened and I noticed it earlier.
    This time I can add that a handful of times when accelerating from a stop w/ only 4 cylinders I would regain full power and correct fuel trims right around 3k+

    Then if I sat at a light for a few seconds 1-4 would drop off again.

    Eventually I lost it for the entire express way ride home.
    Upon arrival I wiggled main engine harness wires, crank sensor wires etc, tapped fuel rail to try to dislodge a potential clog, nothing restored cylinders 1-4.

    Will check again in the morning when I head out to rebuild my 318ti

    I'm leaning towards wiring or dme issues due to the nature off the symptoms... As soon as my E36 compact is running I'll put my e34 in the shop for clutch, differential, suspension and engine work... I hope I don't burn my valves

  2. #2
    Join Date
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    hiss by my window
    Look for something common to all cyls. on that bank. The 12v power to the injectors would be the first place I'd be sniffing around. Perhaps o2 sensors run amok.
    I know PO had issues(confusion) with o2 sensor wiring, I think there may be splices.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  3. #3
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    Update* this morning on file start the car was fine and remained so for the 10min drive to work. On the ride home it was fine

    Thank you Ross for that information it might prove helpful.
    One thing to keep in mind is I don't think the o2 sensor could lean it out as badly as it is. I'm reading the fuel trim off of my wideband gauges, on top of which it seriously is running on 4 cylinders when condition is present. Feels like no fuel what so ever.
    Last edited by Billyj; 04-23-2018 at 12:21 AM.

  4. #4
    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
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    Injector wiring sounds likely. Also, there is a resistor somewhere in the ignition circuit that cracks after a few decades of use. It may be specific to each cylinder bank. Pop open the wiring boxes on that cylinder bank and have a look.

  5. #5
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    Two knock sensors we're completely trashed on the driver's side cylinder bank.
    Passenger side was just cracked

  6. #6
    Join Date
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    I also discovered a partially destroyed wire harness, the aux fan started rubbing through harness directly in front of it, probably unrelated but it's possible something shorted over a bump, discovered this purely by accident when I also found a crack on the inside only of the upper oil pan.

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