Coil Problem

[ricksl1]

once a year...here we go again....coil overheated -shut down ( 300 ft from dock !!) rebuilt '82 228 -305 mercruiser (GM) every year is another new coil ,have checked everything i know to do . 9.5 to the coil (must be inline resistor) ....thing i don't understand is why they mounted the coil right on top of a 170 degree engine. oil cooled coil just not holding up. went with the pertronix pointless system 2 yrs ago...the only thing i can think to do at this point is the pertronix coil (higher output w/ lower resistance ??) anyone else in here had a simular situation ??
Thanx for any info
rick

 

[CharlieB]

Re: Coil Problem

Are you measuring that 9.5V running or just with the key ON?

If that is a running reading then that supply wire is a resisted lead, lowering the voltage to the coil and really should be replaced with a regular wire as the Pertronix unit does function better with a true 12 V supply, then either use a ballast resister or an internally resisted coil.

1982, Merc should have also had a (?) tan wire from the outside terminal of the solenoid to the + side of the coil, by-passing the resisted wire to provide a full 12 V to the ignition during cranking.

Killing a coil every year makes me think that you have been running the wrong coils, check primary resistance, running an internally resisted coil when you should have been using an external resister type coil will cause excessive amp draw through the coils and shorten their life.

 

[CharlieB]

Re: Coil Problem

Also, what plug gap are you using, 0.032, any more causes secondary voltage to rise and contributes to coil loading/heating.

 

[ricksl1]

Re: Coil Problem

let me back up here..come to think of it i did run a new wire from switch....let me run the test over again ...I was running an external resistor required coil....the one i just bought (Napa) is "no external resistor required"...and now batt is low 11.57 (playin with trim motor !!) so i'm only seeing 10.87 to the coil....so really with the pertronix point it should it be 12v to coil/no external resistor ??...dosent say anything about the internal...what should i use...what should voltage be when running?...
Thanks

 

[ricksl1]

Re: Coil Problem

that is only with switch on/ not running....let me get my dang clothes on ...I'll be waiting to hear from ya ...oh and the other thing the nite before last when i was out (300 ft from dock and current pushing me further) I got my boy to put some ICE on the coil after a few mins hit the key ,it fired right up and got me to the dock

 

[CharlieB]

Re: Coil Problem

The Pertronix ignition wants to see 12 V, EITHER coil will work, HOWEVER, a NON-resisted coil needs a ballast installed between the + post and the 12 V source, power the Pertronix unit from the ignition switch side of the ballast resister, , the Pertronix is connected directly to - side of the coil.

A resisted coil just install the Petronix directly to the coil terminals.

NO RESISTANCE in the lead from the ignition.

You need to determine if the power supply is resisted or not. Both will register 12 V key ON engine NOT running, test voltage with engine running and it clearly indicates if it is resisted.