Re: What's up with these 8N coils????!!!!

Posted by GMorrison on August 29, 2004 at 14:40:42 from (68.80.187.196):

In Reply to: What's up with these 8N coils????!!!! posted by Gary Clark on August 29, 2004 at 13:58:48:

Chronic coil failure is usually caused by one of two things -

Either you are running a coil that requires an external resistor on 12v, or you have an incompatible coil/condenser.

While the engine is running check the voltage at the positive side of the coil - it should be in the neighborhood of 6v. If it is, then I would replace the condenser (again if necessary) being sure to use the correct part by production date as your coil, and in your case the wiring harness.

If you have 12v at the coil while running there are a number of possibilities. One is that your tractor was designed to use a coil with an INTERNAL resistor. If this is the case there will be no external resistor in the circut, and from your description it sounds as if there is. The second possibility is that there is a problem in the wiring, possibly a by-pass wired in by a previous owner. The third possibility is that whatever component serves to switch the voltage feed from 12v to 6v is malfunctioning. On some applications the ignition switch has contacts to provide this function, on others either the starter or starter relay provides the switching function. A good wiring diagram will be helpful - hopefully one came with your new harness.

The reason for all this is that ALL ignition coils are essentially 6v coils. (Yes I know there are 12v coils but all these really are is a 6v coil with an internal resistor). On 12v vehicles that don't use an internal resistor coil, some form of external dropping or ballast resistor is used. Chrysler favored those big white porcelean resistor most of us are familier with. GM used a dedicated wire from the ignition switch to the coil which had a high resistance built in (if this wire is replaced with regular wire the problem of short coil life will be the result). Ford used both systems. Engineers took advantage of this situation by creating by-pass circuts that provided 12v to the coil when the engine was being cranked. This provided both a hotter spark and insured that even with a low battery a minimum of 6v would reach the coil. In some instances this altenate circut is energized in the ignition switch, some are done in the starter relay, and others use a contact in the starter.

Hope this helps

Gregg

Follow Ups:

• Re: What's up with these 8N coils????!!!! Gary Clark 19:48:37 08/29/04 (1)
  • Re: What's up with these 8N coils????!!!! TheRealRon 06:38:49 08/30/04 (0)

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