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Low rpm misfire under load. S90-V90 1997

posted by  anarchyx34 on  Mon Nov 5 16:08 CST 2007
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last visit: Thu Feb 21 03:14 CST 2008
[RELATED]

Car is a '97 960. For a while I've been experiencing a low rpm miss under load. It only is apparent under 2k rpms, so the only times I feel it are when taking off and if I open the throttle a decent amount at about 40mph with the torque converter locked up. It definitely seems like a spark miss as it's quite erratic and harsh. It also comes and goes (seems to be correlated with humidity, which again, seems ignition related). I've been hoping i could get it to miss bad enough to set a P030X code so I'll know what cyl to look for but it's not constant enough for that to happen. So i guess the next step is pulling all the coils out and visually inspecting them. Some background info. The plugs and the intake manifold gasket have about 15k miles on them.

Are there any common tell-tale visual cues to a bad coil on these cars?








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    Low rpm misfire under load. S90-V90 1997

    posted by  anarchyx34 on  Thu Nov 8 06:45 CST 2007
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    last visit: Thu Feb 21 03:14 CST 2008
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    Well I pulled the coils. Every single one of them was cracked all the way through. Only one of them had carbon tracking indicating arcing. Taking from my past experience with VW VR6 coil packs I epoxied the sh*t out of them. I'll find out later tonight if it actually fixed them. At $50 a pop I hope so.








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    Low rpm misfire under load. S90-V90 1997

    posted by  david hunter on  Tue Nov 6 14:33 CST 2007
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    last visit: Mon Jun 30 22:10 CST 2014
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    I have had code PO30x on various cylinders over the years on my 97 V90. It was spark plug twice and a coil once. I am surprised that you have not had the CEL light come on with set code. When I had the spark plug miss both times it was so intermittent that I did not even notice except that the light came on. Of course when the coil pack went bad that was very obvious as it was a solid consistent failure. There were no obvious external signs of failure on the coil pack nor was there any measurable difference in resistance on the 2 input (primary) pins between the bad coil and a good one. Did not check the output (secondary) though. I just replaced it with a used one from the wreckers.

    It may be that when the rpm's are in that higher range the miss cannot be detected. Maybe the only way is to swap the packs one at a time.
    --
    David Hunter








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    Low rpm misfire under load. S90-V90 1997

    posted by  DanR on  Tue Nov 6 04:28 CST 2007
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    last visit: Thu Oct 23 15:25 CST 2014
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    Maybe a vacuum line was missed when the intake gasket was replaced. Sounds like you have a leak somewhere, inspect all of the hoses, and look at any rubber bends, they will sometime degrade and allow for air to leak.

    DanR '94 332,000 miles (98,000 on the new engine)
    --
    DanR








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      Low rpm misfire under load. S90-V90 1997

      posted by  anarchyx34 on  Tue Nov 6 05:54 CST 2007
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      last visit: Thu Feb 21 03:14 CST 2008
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      Definitely not a vacuum leak. This is clearly a spark miss. I'm just wondering how these coils typically fail so I can know what to look for when I pull them all out.








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        Low rpm misfire under load. S90-V90 1997

        posted by  DanR on  Tue Nov 6 08:19 CST 2007
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        last visit: Thu Oct 23 15:25 CST 2014
        [RELATED]

        I have read that when they go they'll have small cracks, also read that the earlier models, pre OBDii coils were more durable and resist the heat of the engine better than the newer models so your does fit that description. So you maybe on to something, if you can isolate the miss to one cylinder it should be easy, if that fails, maybe it is a bad power stage, the key is getting it down to a cylinder though.

        DanR '94 964 332,000 miles (98,000 on the new engine)
        --
        DanR








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          Low rpm misfire under load. S90-V90 1997

          posted by  volvosenior on  Tue Nov 6 14:55 CST 2007
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          last visit: Tue Oct 21 21:49 CST 2014
          [RELATED]

          start the car and let it run or run it until you can detect the misfire in the ignition. stop the car, open the hood, and feel the exhaust manifold(carefully)
          on each cylinder. if one is a little cooler that the others (you'll be able to tell)that's the one that is misfiring. don't know much about the coils you refer to, but check the plug wires for continuity. sometimes the wires just stop working unexpectedly-








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          Low rpm misfire under load...power stage??... S90-V90 1997

          posted by  B.C. on  Tue Nov 6 09:51 CST 2007
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          last visit: Wed Mar 28 22:28 CST 2012
          [RELATED]

          An earlier post about 960-S/V90 ignition suggested that swapping the two power stage units can reveal which group of cylinders has the problem. The PS units "feed" cylinders #1-2-3 or #4-5-6.

          My parts guy told me that a coil pack can develop a visible crack. If (and when) you change the plugs, give each pack a close look. There is a narrow part that is the first place to look.

          Good Luck,

          Bob

          :>)








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    Low rpm misfire under load. S90-V90 1997

    posted by  someone claiming to be qmechanic on  Mon Nov 5 17:46 CST 2007 [RELATED]

    You may also check the intake manifold gasket.It is known problem with this model.
    Similar symptoms.

    qmechanic







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