I have just purchased a '76 F250 with a 390 and electronic ignition. I have since lost 5 coils in less than a month. I am not sure which electronic system is in the truck..but the control box is aluminum with ribs on half of it, also it has the small distributor cap. I have checked the voltages and with the engine off the voltage at the coil is 8v at idle 10.5v... I have since put a block resistor in and that dropped the voltages to 6v and 8.5v. That didn't work either because I lost another coil today.
Also the battery voltage is 12.5 and 13.5 to 14 at idle. I did notice that at a moderate RPM the voltage will climb to about 11.5v. It has a new alternator and a duel battery system w/camper special setup. Anyone have any ideas on why I keep losing coils?


Thanks for any help!!! Chris

 

Chris, those voltages sound about right. The only things I can think of are to check to see that your power wire coming from resistor is connected to + terminal of coil, and make sure the coil primary wire has good connections at coil post and at distributor post, and that the coil wire itself is good. You may have too much resistance between coil and dist, thereby overheating the coils. Good luck.

"Nothing lasts forever except natural stone and old Ford trucks." (Willie Nelson)