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Thread: M50 Occasional Misfire

  1. #1
    Join Date
    Jul 2015
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    Oceanside, California
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    135
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    1994 325is

    M50 Occasional Misfire

    So i've been running into this problem with my new drift build, where after beating on the car for about 10 minutes sometimes it will just kind of bog out and misfire. It mainly happens literally in the middle of a drift, so my initial thought was some sort of oil starvation, but i've always ran my drift cars half a quart over full and I check the level each time it happens. Always full. So i'm starting to think maybe I have a loose connection on a coil pack? Spark plugs are brand new. Every time it happens I stop drifting and kind of just rev it up in neutral or drive normally until it goes back to normal. Only takes like 10-15 seconds to go back to firing on all 6 each time so its not a MAJOR problem that prevents me from drifting, but i'm worried it'll become a lot more prevalent when I actually get it out on some track days and hot lap it. (Southern California tracks are regularly 90-100 degrees) Ive had another M50 in a drift car before and never ran into this problem, and that motor saw tons more abuse than this one has, so far... Its a 1994 325is with an M50 vanos motor and getrag 5 speed. Motor is stock with exception of turner motorsport underdrive pulleys and an exhaust. So i'm thinking its just the coil packs or something else small and dumb, but I wanted to get some input from you guys first. thanks.


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  2. #2
    Join Date
    Dec 2013
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    EXOTICS
    I'm thinking something causing fuel starvation,
    try checking fuel pressure,
    or right pump and left fuel level sensor.

  3. #3
    Join Date
    Jul 2015
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    Oceanside, California
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    1994 325is
    Quote Originally Posted by MIKYZZ4 View Post
    I'm thinking something causing fuel starvation,
    try checking fuel pressure,
    or right pump and left fuel level sensor.
    Fuel pressure was good, pump seemed to be working fine and at correct voltage. For whatever reason I still feel like its related to the oil, but open to more suggestions. Car runs completely normal when driving under normal conditions, or even doing pulls its fine, only acts up when drifting. (weight transfers over and over)

    I also forgot to mention that I think the VANOS is failing/doesn't work. Idle drops a lot and isn't consistent with AC on, and I can feel it drop off at about 4500rpm as if the vanos worked for a second, then you can feel it get slightly slower. Not sure if this is related to my misfire problem.

  4. #4
    Join Date
    Apr 2016
    Location
    Detroit, MI
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    1997 328i, 89 325ix
    Try swapping your coil packs around and see if it still does it. Does it always do it on the same cylinder, or is it random?

  5. #5
    Join Date
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    Austin, TX
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    S13, Turbo M3
    Quote Originally Posted by keramnitsuj View Post
    Fuel pressure was good, pump seemed to be working fine and at correct voltage. For whatever reason I still feel like its related to the oil, but open to more suggestions. Car runs completely normal when driving under normal conditions, or even doing pulls its fine, only acts up when drifting. (weight transfers over and over)

    I also forgot to mention that I think the VANOS is failing/doesn't work. Idle drops a lot and isn't consistent with AC on, and I can feel it drop off at about 4500rpm as if the vanos worked for a second, then you can feel it get slightly slower. Not sure if this is related to my misfire problem.
    Oil sloshing won't cause an ignition related misfire - it has to be something electrical or something else. Sounds like fuel starvation but it's really hard to pin point. Does it do it with a full tank, or only when the fuel is low? Are the coil packs new or old? Do you have any codes? New plugs? The only thing oil sloshing can do is cause the oil pressure to temporarily drop, but that will have no effect on the misfire/combustion side of things.

    Mike
    IG: @mikevanshellenbeck

  6. #6
    Join Date
    Jul 2015
    Location
    Oceanside, California
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    1994 325is
    Quote Originally Posted by MikeE36 View Post
    Oil sloshing won't cause an ignition related misfire - it has to be something electrical or something else. Sounds like fuel starvation but it's really hard to pin point. Does it do it with a full tank, or only when the fuel is low? Are the coil packs new or old? Do you have any codes? New plugs? The only thing oil sloshing can do is cause the oil pressure to temporarily drop, but that will have no effect on the misfire/combustion side of things.

    Mike
    Thank you for the input, Ive taken the car out for a few street seshes since I started this thread and it hasn't happened again.... I'm trying to narrow down the possible causes but i'm thinking it might only happen when the tank is full. I'll update this thread if i find out what the cause is.

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