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Old 07-13-2008, 08:11 PM
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coil killer?

I have a 1985 f150 pickup with a stock 302 . something is frying my ignition coil i have replaced 2 in the same day. When i installed the second one the truck started right away so i shut it down to clean up, about 1 and 1/2 hours went to start the truck and the coil was 'nt putting out spark again.
there is power geting to the coil.i also changed the spark box just in case. The battery is not holding a charge or is being drained .could the 2 be related or just a coincidence ? i have no idea what could fry a coil so quickly ??? thanks for any help ........

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Old 07-13-2008, 09:31 PM
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If the coil came from Auto Zone, Advance Auto, etc the new coil very well could be bad, been there myself. When you checked the power to the coil was it getting 12 volts? It should have only about 8 volts but even if it is full voltage I doubt it would cause problems that fast if at all, some people even run 12 volts all the time.
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Old 07-13-2008, 09:37 PM
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Does the coil have a built in resister,?
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Old 07-13-2008, 11:40 PM
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Are you sure its the coil and not the ignition module. They can act up when hot and work again after cooling off. Just a thought.
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Old 07-14-2008, 10:28 AM
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When you turn the key off make sure the power to the coil also turns off. It could also just be a bad replacement coil. When you crank the engine does the negative side of the coil pulse. If not there is something else wrong.

Coils are not high failure rate items


Chet
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Old 07-15-2008, 04:00 PM
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coil killer

I have changed the coil twice sence then they keep frying???? it's geting 12 v at the coil but it has been that way for 7 years and i never lost a coil b4 . When i take the key out of the ignition and unhook the battery i'm getting little sparks like i left something turned on but every thing is off. with the key off the power wire to the coil is dead so its not that wire at least . could the voltage regulator be frying my coil . the volt gage is dead in the center where it should be. and i get 14.2 at the battery when it actually runs..... still lost any more ideas help thanks omega......
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Old 07-15-2008, 06:00 PM
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Not saying that for sure is killing your coils but you should have only about 8 volts on the coil. This is done trough a resistor in one form or another depending on make but it is because that is what the voltage drops down to when the starter is engaged. There will be a resistor by-pass circuit that will allow full voltage to the coil during cranking to keep it from getting less than 8 on the resistor circuit during the cranking mode, this full voltage circuit would itself be only about 8 volts during cranking and would jump to full battery voltage when the starter load is released but when that happens that circuit is dropped out and will no longer feed the coil. If you are getting a full 12 volts to the coil with the key in the run position the voltage to the coil is too high.
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Old 07-16-2008, 05:38 PM
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re coil killer

Thank you all for your advice ....i don't know if there is a resistor circuit some ware in the system or even where to look for it .. but i had no trouble with the ignition system for 7 years so if there is a resistor some ware i guess it must have failed .. can i put a resistor in the power wire to the coil or does it need to be controlled by something along the way ?? does the computer control it or the ignition module ?? so the resistor bypass circuit works... I changed the ignition module again and try-ed the three fried coil's again and got no spark from either one so i guess the module is OK .. (my coil is a canister type if that matters.. thank s again all ....
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