Burning Up Coils

[Fishaholic247]

I have a '87 4.3 Mercruiser with Thunderbolt ignition that keep burning up coils. I had a Mercruiser long block put in by local shop in March. They also installed new spark plug wires, cap, and rotor button along with many other new parts (all Mercruiser parts no aftermarket parts.) After we determined it was burning the coils the owner of the shop called Mercury Tech. and they told him to look for a carbon trail in the in the coil wire and if it was present that a Accel coil wire would fix the problem. It was there and Mercury paid for a new coil and the Accel coil wire but, it is still burning up coils after this "fix". I am hoping that someone else has come across this problem before and has a solution for it. I left the boat at the shop this morning after getting off of the water for the mechanic to try and find the problem but was thinking maybe I could do a little research and help him out in hopes of getting my boat back sooner. Any and all advice is deeply appreciated!

 

[Bt Doctur]

Re: Burning Up Coils

might try measuring the voltage on the + side of the coil with the motor at say 2500rpm.

 

[Fishaholic247]

Re: Burning Up Coils

Thanks for the reply! We did that last night and it was reading 13.7 volts.

 

[Fishaholic247]

Re: Burning Up Coils

ttt

 

[Mischief Managed]

Re: Burning Up Coils

Pretty sure you are supposed to have a ballast resistor in-line with the + lead on the coil to drop the voltage for normal running. The ballast is only by-passed for starting, when the started draws the battery voltage way down.

 

[lonemust]

Re: Burning Up Coils

Yesyou need a ballast resistor you are get to much volts to the coil. When key is run posistion you should not have more the 9 volts. Easy fix put in new coil and a BALLAST RESISTOR, this will cut the voltage down to where it needs to be.

 

[180shabah]

Re: Burning Up Coils

TB4 has no external resistor.

 

[JustJason]

Re: Burning Up Coils

Only points use an external resistor, and that's to keep the points from burning up, not the coil.

Is the coil mounted in the factory location or did somebody move it? Is the inside doghouse getting excessively hot?

 

[Fishaholic247]

Re: Burning Up Coils

The coil is mounted on the back of the port side of the motor. I don't believe the doghouse is getting excessively hot. I opened it up the other night while my fishing partner was driving I checked for spark escaping from the coil wire and didn't see any but, didn't feel any excessive heat either.