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Thread: Mystery Miss

  1. #1
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    02HD9294's Avatar
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    Mystery Miss

    Now that I have your attention.....

    I had been experiencing a bad misfire under load (not necessarily on boost either) and decided that it was time to change the plugs. 160000 km on the odometer, (I bought it at 60000 km) so it was long overdue. Old plugs were found to be quite fouled and worn, so that was definitely the main cause of the poor performance.

    Tech at the dealer is a Roush specialist so I felt that I was in good hands. After plugs were replaced (torqued correctly - I even left him a reminder note), on-road diagosis found a random misfire on the front two cylinders on passenger side and the front cylinder on driver side (1, 2 and 4?). Misfire only happens under load (again not necessarily boost) and doesn't raise a code. The tech swapped COP's and injectors around per normal practice but the misfire stayed with these three specific cylinders. Hotline advised him to clean the MAF which he did with some effect. Had them check for vacuum leaks and none were found. Told the shop not to go any further, (their hourly rate is a crime) and that I would drive it for awhile and monitor the performance.

    The truck accelerates great now - very smooth with a lot more kick and cruises great, but on occasion there is this little hiccup that can be felt only under load as described above. I don't punch it unless I'm merging onto the highway or have to pass on a hill.

    Truck is completely stock. I'm wondering if the problem is electrical, originating in the PCM. Anyone else experience this phenomenum? Any thoughts on the electrical being the problem?

    Thanks,

  2. #2
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    Name: Byron

    GRANTBP's Avatar
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    i had that problem it was COPS you said they are all new check the connections i would have them run a D C check i did not show any codes but under aload the codes show up good luck

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    cayman150's Avatar
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    A dealer should have the proper tester to check the COPS 'under load'.

    I had mine tested on one of those Ford machines and they showed good under the normal check and at idle but when put 'under load' there were about half that showed break down on the graph and did not put out the correct voltage in a consistent manner during the entire RPM test range.

    I replaced all 8 and got a pretty good deal on OEM Motorcraft ones from RockAuto.

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    Thanks. That makes the most sense, as 7 of 8 COP's are originals and probably getting tired. Truck is running pretty well right now so I'm going to drive as-is for now and replace them in the spring.

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    def replace your cops roger, sometimes they get brittle and will only thow missfires once and awhile.
    i repaced 2 of mine at 9k, then at 12k i went with weapon x coils becuase i didnt drive it in the rain.
    2002 HD #8339
    ......sold but not forgotten
    2007 CTS V
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    kooks , corsa and a few other goodies

  6. #6
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    the technician should only get paid to diagnose the concern one time, It is not pay as you go. and he should of told you to put new coils in the first time. instead of messing around with it.

    In his diagnosis, if he was swapping coils and plugs and injectors, that should all of been free and included in his 1hr diagnosis.............. not i want this and that and oh im gonna do this but your gonna pay for all of it............ thats not how it works in this business....

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