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Thread: Bad Coil???

  1. #1
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    Jun 2007
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    Columbia, SC.
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    335

    Default Bad Coil???

    How do you know if you have a bad coil in the ignition system?? How do they general fail?? What are the symptoms? Is it a go or no-go situation??

    I Think mine is failing, but it could be something else. Trying to trouble shoot the coil first, then tackle other components if the coil is okay.

    Thanks,

    Jim
    1978 CJ-7, Amc 401, 4" lift, D30/T-176/D300/Amc 20
    35" x 15.5" Super Swampers on 15x10's

  2. #2

  3. #3
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    Jun 2007
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    Columbia, SC.
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    Default

    Seriously, none of you ole time mech NEVER had a coil go bad???

    Experiences...Experiences, please.
    1978 CJ-7, Amc 401, 4" lift, D30/T-176/D300/Amc 20
    35" x 15.5" Super Swampers on 15x10's

  4. #4
    Registered
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    May 2004
    Location
    Monroe, WA
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    508

    Default

    Loss of power, hard to keep at idle. Would occasionally die but would start back up after a minute of two. This was a MSD Blaster coil with a HEI module. Something was shorting in the coil, just enough to overheat the HEI module and shut it down. Thought it was the module so I swapped that first but ended up being the coil.
    86 CJ7, 258 w/4.0 head, Clifford w/ Holley 390, TFI-HEI hybrid, 4.10 gears, 4" lift on 33's, Woody shaft, locked at both end, keepin' it simple

  5. #5

    Default mine..

    I had a coil go bad once. it would run untill it got to run temp. and would quit. then once it cooled down it would run again. which is a classic sign.It took me couple days to figure it out the first time.
    -77' Jeep cj7, 360/t-18/dana20/hp d60's arb's 4.88/
    39.5 tsl's
    -85' Jeep cj8 ,*(project justed started)*

  6. #6
    Registered hozercj7's Avatar
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    Mar 2005
    Location
    Dayton Ohio
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    478

    Default

    the way i found out i had a bad coil was...
    I used my timing light while carnking over the motor.
    Just hook up the timing light to the coil wire instead of the number 1 spark plug wire and crank it over. If the light blinks you are getting spark to the dist. if it doesnt blink you coil isnt putting out spark.
    There could be other problems but this might help.
    86 CJ7 RE4.5 Extreme duty lift OBA TSL33 SuperSwampers 2400watt power inverter Winch Woody CV driveshaft 4.56 gears detroit in the rear
    and building

  7. #7

    Default

    It's almost classic coil problems if the engine just cuts off at idle for no apparent reason.

    No chugging, no trying to run, just shuts off like you turned the key off. Usually starts right back up.

    Other symptoms will include a general sluggishness at part throttle cruise, and some times random misfires at or near wide open throttle.

    You may get some 'Hard Start' problems with the vehicle is very cold or very hot, but this is unusual with Ford type coils.
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