What Problems With Bad Coil

Discussion in 'Fox 5.0 Mustang Tech' started by 79dog, Sep 8, 2013.


  1. 79dog

    79dog Founding Member

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    The car has been Idling rough and stalls now and then. Pulled the coil wire off and touched it to ground and turned the key on. The spark is yellowish orange. Most of the info I find says the spark should be blue. Does this sound like a bad coil?
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  2. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    factory ignition or msd stuff? Coils usually just die, not fade out
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  3. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    I had only one problem with 5.0 Fox Mustang ignition coils, and it was very difficult to diagnose. The car would only start intermittently, and ran poorly when it did start. Since the EFI ignition coils were cheaper at that time, I now have a spare to swap.

    The cost of a replacement coil for your car looks to be in the $18-$28 range, so if you can get one from the junk yard it might be much cheaper.

    Prior to replacing the coil, do some simple checks like making sure all the electrical wiring is in good shape and the connections are clean and not loose or corroded.

    If I am not mistaken, you car came with a DuraSpark system. Here's a diagram for it...
    Duraspark II ignition diagram:

    Diagram courtesy of /www.billwrigley.com
    [​IMG]
    See http://webpages.charter.net/1bad6t/duraspark.html for more help.
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