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Thread: Ignition issue?

  1. #1
    Join Date
    Mar 2021
    Location
    Ottawa, Ontario
    Posts
    3

    Default Ignition issue?

    Hey guys,

    An issue has surfaced and I am looking for possibilities of what it could be.

    Car Info: Volvo XC70 2004, 302000 KM on it.

    When driving on the highway(with cruise and without) the car seems to buck, like basically hitting a bad bump in the road, then it picks it back up and starts driving normal again. Ive noticed it seems like it happens when the car demands power(IE going up a hill) but I cannot confirm this is the case everytime. All was fine on my drive up(about 600KM) but on the way back this issue happened about 6 times total. This definitely feels like an ignition issue, I am wondering if there is a way to diagnose this, or if there are some things I can check before actually trying to change parts. I have read another forum where the person seems to have the same issue I do and they changed to coils and plugs and that fixed it but I wonder if it could be something else that I can easily check or if I should just change the coils and plugs and go from there.

    Any help will be greatly appreciated!

  2. #2
    Join Date
    Mar 2021
    Location
    Ottawa, Ontario
    Posts
    3

    Default

    Forgot to mention when this "Misfire"/"Buck" does not produce an engine code.

  3. #3
    Join Date
    Dec 2009
    Location
    GA
    Posts
    1,402

    Default

    If it's not fuel or ignition related -

    The CEM on some cars overheats and can cause that symptom on hot days, during longer trips. You could try removing the underdash panel on the drivers side to allow more air to circulate - Companies such as xemodex add heat sinks to the CEM to combat heat related failures.

    Courtesy of xemodex -

    "Common Communication Failures:
    The following failures are almost always intermittent in nature, meaning that the CEM will operate normally most of the time. To reproduce these symptoms, start the vehicle and heat up the CEM with a hair dryer for about 5 minutes, and observe the instrument cluster for any abnormal operation.
    • Low Speed bus failures where two or more control units suddenly stop working at the same time. Most commonly the instrument cluster shuts down and the operation of power windows and sunroof is not possible. This is very common for all 2004 Volvo models with CEM part number 8688513."

  4. #4
    Join Date
    Mar 2021
    Location
    Ottawa, Ontario
    Posts
    3

    Default

    Hoonk, this diagnosis actually would make sense with how the car was acting yesterday. It was extremely hot over the weekend and at the beginning of the weekend this issue did not happen at all but as the weekend went on and the hotter the weather got is when it started happening.

    Do you think this would have caused the issue of the dashboard not working after turning the car off and trying to turn it back on? Because that also happened the same day this "Bucking" issue happened.

    Hoonk you're the man! You really put my mind at ease.

  5. #5
    Join Date
    Dec 2009
    Location
    GA
    Posts
    1,402

    Default

    Quote Originally Posted by Ipwnedbarney View Post
    Do you think this would have caused the issue of the dashboard not working after turning the car off and trying to turn it back on?
    Yes, a quote from Xemodex "Most commonly the instrument cluster shuts down" .

    I've experienced CEM problems in customer cars - one malfunctioned on the expressway - it felt like I had gone over a speed bump at 70 mph.

    It's not cheap to fix - but with increased ventilation you may keep it cool enough to prevent malfunctions

    https://xemodex.com/us/product/centr...ansferservice/

  6. #6
    Join Date
    Aug 2017
    Location
    Pleasanton CA USA
    Posts
    484

    Default

    I had this exact problem with my 2004 XC70 2.5T at 120K miles. The engine "kicked" only when I was driving above 60 mph, and was trying to accelerate.

    I replaced the coil-packs and spark plugs, and that solved the problem. In terms of previous maintenance, there was no record of the plugs ever having been replaced.
    When they came out, the electrodes were worn down nubs, and the gap was 1.5X the spec. The recommendation is new plugs every 40-50K miles.

    As far as needing new coil packs, that was just a guess on my part, but they were original equipment, and should be replaced every 100K miles or so.

    There were never any DTCs thrown.
    2013 XC70 T6 Flamenco Red (hers)
    2015 XC70 T6 Seashell Metallic (his)
    past: 13 Volvos going back to '74 242 sedan

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