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Hop and a Skip - Why? 900 1994

posted by  Townshend Act on  Tue Oct 3 00:22 CST 2023
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last visit: Tue Oct 7 22:44 CST 2014
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My beloved B230FT runs great, except when idling in drive at a stop.
Every 20-30 seconds, it give a quick single misfire. Then today, it displayed the same condition under acceleration onto the freeway today. Again, between every 20-30 seconds. At normal cruising speeds I do not detect any misfire, and the engine performance is otherwise very strong.
Feels like a spark issue. No vacuum leaks detected, and all electrical connections are sound.
Am I over-thinking by suspecting the Mass Air Sensor, or could it be as simple as a spark plug or plug wire?
Occurs at normal operating temperature with or without the A/C engaged.
Don't know why I'm drawing a blank on this one.
Any help out there friends?
1994 Volvo 945T w/AW-72 transmission.








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    Hop and a Skip - Why? 900 1994

    posted by  spook on  Tue Oct 3 01:22 CST 2023
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    last visit: Fri Oct 24 08:06 CST 2014
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    Dear Townshend Act,

    Hope you're well and stay so. When were the distributor cap and rotor last changed?

    It sounds - literally - as if skip frequency has just increased. I wonder if there's a "burned" spot on the rotor, that slowly grows.

    Hope this helps.

    Yours faithfully,

    Spook








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      Hop and a Skip - Why? 900 1994

      posted by  Dave Stevens on  Tue Oct 3 14:35 CST 2023
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      last visit: Sun Jan 1 02:36 CST 2012
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      Agreed, worn distributor cap/rotor and I'll add also ignition wires poorly seated or otherwise not making for a good spark
      --
      Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now








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        Hop and a Skip - Why? 900 1994

        posted by  Townshend Act on  Sat Oct 7 00:40 CST 2023
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        last visit: Tue Oct 7 22:44 CST 2014
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        Great to hear from you again Dave. I think I located my issue in a worn plug wire likely grounding on the valve cover. Luckily this discovery was made by sound and flash, and not a bodily encounter, if you know what I mean.
        All the secondary ignition (Cap, rotor, wires and plugs) are less than 5 years old, with fewer than 10,000 miles of use.
        As is my style, everything from the rotor onward to the spark plugs are planned for replacement.
        FCP Euro is supplying everything OEM or Bosch, and is expected next week sometime.
        I truly appreciate your interest and responses to my queries. It what has made the Brickboard work for these many years. Thanks for helping me keep the Red Block in top condition. Take care Dave.
        John








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      Hop and a Skip - Why? 900 1994

      posted by  Allrounderco on  Tue Oct 3 06:52 CST 2023
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      It's more difficult to generate a fat spark as cylinder pressure increases. As you are generating the most boost under hard acceleration, the fact that the issue presents itself then indeed suggests an ignition issue.

      As Spook recommends, I'd start at the cap / rotor, and work back toward the plugs from there. Given your car would have the distributor run off the back end of the cam, there's also the possibility of oil getting in the cap. Resealing those is inexpensive, and there are a few how-tos on here with pics, if you haven't had the pleasure (infer sarcasm) of doing that job yet. When I had this happen, I was able to clear the issue up temporarily by cleaning out the oil real good. It lasted until my order of the requisite O rings and fiber washers showed up in the mail (FCP). I also refreshed the cap/rotor, plugs, and wires at the same time. They were probably fine, but now I have spares for troubleshooting.

      Hopefully it's just a worn plug, as that's also cheap, and the easiest to remedy.








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        Hop and a Skip - Why? 900 1994

        posted by  Townshend Act on  Sat Oct 7 00:32 CST 2023
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        last visit: Tue Oct 7 22:44 CST 2014
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        Thank you very much for your detailed explanation. I believe i found a chafed plug wire to #2 cylinder, capable of shorting occasionally on the valve cover. The Brickboard members owe a debt of gratitude to you guys for reaching out and helping fellow members with whatever issues they have.
        Much obliged.
        John







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