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  1. #1
    FEP Power Member dagenham's Avatar
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    Default MSD coils and spark plugs

    I ordered a set of MSD street fire coils for my wifes '04 Mach 1 today and I'm thinking should I get spark plugs that are a step hotter or just get factory replacement plugs?
    What do y'all think?
    Current Mustangs
    1966 6 cylinder coupe
    1984 SVO 9W
    1985 Saleen #132

  2. #2
    FEP Senior Member Greywolf's Avatar
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    I'm fond of one change at a time unless the manufacturer of the product recommends the additional change (then I count it as part of the one change). If it's just the coils and there's no change in tune, I'd just install new factory-spec plugs and make a mental note to examine them after a few good drives.

  3. #3
    FEP Power Member dagenham's Avatar
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    That's what I was thinking but I wanted a second opinion.
    Current Mustangs
    1966 6 cylinder coupe
    1984 SVO 9W
    1985 Saleen #132

  4. #4

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    I'm curious what was wrong with the coils that have lasted 15 years? Also if there were no engine components changed, there would no reason to change the heat range of the plugs. It might be a convenient time to change them with a similar plug but there would be no reason to change the heat range. Besides a "hotter" plug would only be used if you are having problems with the engine or it is performing bad to prevent fouling. Are you having that issue? If you are modifying the engine with ported heads, cams etc. it would require a colder plug, not a hotter one.
    Last edited by homer302; 10-16-2018 at 07:33 PM.

  5. #5

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    Also don't forget the anti-seize on the threads if you change them. That is not optional.

  6. #6
    FEP Power Member dagenham's Avatar
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    I can feel a miss mostly when cruising at speed on the highway. Plus the car 168K on it and I don't know the history that well. We just bought a few months ago.
    It's not uncommon for these coils to act up so a little preventive maintenance.
    Current Mustangs
    1966 6 cylinder coupe
    1984 SVO 9W
    1985 Saleen #132

  7. #7
    FEP Super Member erratic50's Avatar
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    Just re-read. 04 coils were notorious for going out if the plug gap opened up too wide. Fresh plugs is good maintenance. Once one coil pack is a miss, expect the others to follow.

    on my 08 Mountaineer I sorta refused to do plugs on schedule and coil packs started dropping like flies. Would swap in a new plug with the pack, 4 failed before I just finished replacing the entire set.....

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