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Misfire...on one, two, then three cylinders 900

uid 15548's pic
posted by  volvo245gti on  Sat Aug 29 11:32 CST 2009
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last visit: Sat Sep 13 16:32 CST 2014
[RELATED]

'92 960...

Last May when we were heading to Portland our 960 had a bit of a hiccup. After filling it at one stop it started to miss. At first it seemed like a bit of a mis-fire but then it got worse and eventually was acting like it was missing on 3 of the 6 cylinders it has. Not only did it seem like it was missing on 3, it seemed like 3 consecutive. The whole car would rock back and forth. It was nasty. Apparently the was black smoke and flames spitting out the tailpipe too. The flames part is relatively important as it points to an ignition problem, not a fuel problem. Anyhow, this went on for a few minutes and then went away...quite abruptly. For the next 400km it ran like a dream. However, after the next fuel stop it did exactly the same thing...and then abruptly stopped again. For entire rest of the week and the entire trip home it ran without so much as a hiccup.

Fast forward a month or two and my wife comes home one day saying the car was doing its thing again. Then again and again. I decided it was time to give something a try so I replaced all the coils and spark plugs. That cleared everything up and the ran ran flawlessly...until yesterday. It acted up for about 1/2 hour and then quit abruptly, just like before. Again today it did it, not once, but twice.

So...some input? I've got a set of coil control modules that will go in this weekend. Anything else might cause this behaviour? How about a bad knock sensor? If the computer was seeing horrible knock would it pull enough timing out to make it start missing? It gets gradually worse. It does not start out missing on 3. FWIW, the control modules control 3 consecutive firings in the firing order. Seems a bit silly to me to do that but the engineers that designed it have a little more knowledge about this stuff than I do so who am I to question? If one module goes bad, it'll miss on 3, fire on 3 etc. Makes for a pretty crazy idle and absolutely no power...

I put one coil module in today (I figure if I replace both, I'll have to toss both old ones out as I won't know which one was the bad one). Now we wait...

Thanks in advance,




--
Dale








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    Misfire...on one, two, then three cylinders 900

    uid 11021's pic
    posted by  dewfpo on  Sun Aug 30 10:29 CST 2009
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    last visit: Thu Oct 23 18:34 CST 2014
    [RELATED]

    The forward power stage controls cylinders 1, 3 & 5. The rear power stage controls cylinders 2,4 & 6.

    The knock sensors are not the problem here.

    Does it ONLY occur after a fuel fill up?

    DEWFPO
    --
    1998 S90 083,228 and 1995 964 154,100








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      Misfire...on one, two, then three cylinders 900

      uid 15548's pic
      posted by  volvo245gti on  Sun Aug 30 12:37 CST 2009
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      last visit: Sat Sep 13 16:32 CST 2014
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      "Does it ONLY occur after a fuel fill up?"

      No...that's when it initially occurred. Since then it seems to be random although it's only when the car has been running for a while so heat soak into the coil modules is certainly a possibility...

      We'll see if it happens again tomorrow when I'll be driving the car for most of the day.

      --
      Dale








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    Misfire...on one, two, then three cylinders 900

    posted by  david hunter on  Sat Aug 29 17:15 CST 2009
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    last visit: Mon Jun 30 22:10 CST 2014
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    I think you are onto the problem. The front module fires 1,2,3 and the back module fires 4,5,6. One or the other goes bad when it gets real hot. The reason it happened on the highway stop was due to "heat soak" The higher internal engine temperature from on the highway drive "soaks" through to other components (in this case the intake manifold) when you shut down.

    I believe they are installed with a heat sink grease stuff.
    --
    David Hunter








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      Misfire...on one, two, then three cylinders 900

      uid 15548's pic
      posted by  volvo245gti on  Sun Aug 30 03:35 CST 2009
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      last visit: Sat Sep 13 16:32 CST 2014
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      We'll see, now that I've replaced what looks to be an original module...the rear one. That's quite a treat to get at, I must say. However, I'm pretty sure the front module does not control 1,2 and 3 but rather 3 consecutive cylinders in the firing order. the rear module controls the other three. I read that in my green book on 960 wiring. This is what led me to think it might be a module. When it starts missing really badly, the engine will rock the whole car, like it's missing on three consecutive firings.

      I suspect the front module has been replaced as it is a slightly different package than the rear. Still Bosch and the same part number but slightly different.

      --
      Dale








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        Misfire...on one, two, then three cylinders 900

        posted by  david hunter on  Mon Aug 31 11:34 CST 2009
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        last visit: Mon Jun 30 22:10 CST 2014
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        You are absolutly correct on the module to coil # relationship. I stand corrected. Hope the new module solves the problem.
        --
        David Hunter








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    Misfire...on one, two, then three cylinders 900

    posted by  stealthfti on  Sat Aug 29 14:54 CST 2009
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    last visit: Tue Jan 28 17:36 CST 2014
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    Dale,

    how old is the crank sensor? It might be a contributor to the problem.

    I had a fun time on a 92 960 that would not start. Went over things fairly extensively. Found the flexplate to be warped about 3 thou [the motor had just been replaced. The replacement motor actually started up once and ran for a few minutes, then died, and would not restart. I was called in after a month of the owner messing and trying things.

    After I checked the flexplate in car and found the warpage, the owner had the trannie pulled and replaced the 'plate. Fired right up.

    ...while diagnosing the prob, the intermittent crank sensor signal would sometimes give me spark to all 6 plugs, then drop 3 and then all 6.

    my point: that crank sensor might be affecting the dropping of those 3 cylinders.

    But, I would go over the wiring for both of the modules inch by inch to make sure that there is not a problem. Because a wiring prob that affects one cylinder can and will affect the other two on that module.

    Been a while since I messed with a 960 but IIRC, one module is fairly easy to access and the other one is a PITA to get to. The way the wiring is routed is not exactly fun to get to either.

    TF







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      Misfire...on one, two, then three cylinders 900

      uid 15548's pic
      posted by  volvo245gti on  Sun Aug 30 03:43 CST 2009
      Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
      last visit: Sat Sep 13 16:32 CST 2014
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      Thanks for the response TF.

      I suspect the crank trigger might be original. This car doesn't have a ton of miles on it and the engine and tranny have never been split. Was asking Matt about a cam or crank trigger and he gave me a reasonable explanation why he thought not. So, for the time being, I'll dismiss that. I also suspect the crank sensor is what triggers the coil modules. If there was an intermittent signal it would drop 3 or 6, never just 1 or 2, which is how this starts out.

      The wiring on that car is in very nice shape. I have not inspected it closely but will start to trace things back if my current fix does not cure the problem.

      Cheers,

      --
      Dale








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        Misfire...on one, two, then three cylinders 900

        uid 15548's pic
        posted by  volvo245gti on  Mon Aug 31 12:00 CST 2009
        Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
        last visit: Sat Sep 13 16:32 CST 2014
        [RELATED]

        Drove the car around town for 7 hours today and not a hiccup. Seems like we may have busted this one...

        Thanks for the suggestions guys...

        --
        Dale







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