[DeTomaso] Dura-spark key-on coil burn-up fix

Wed Jun 27 23:50:15 EDT 2007

I believe this is a problem with the Duraspark and not related to the 
resistor.  Several years ago I burned out my coil while I was replacing 
a window gear.  I left the ignition on, but never started the car.  I 
was just testing the window with the window switch.  Went to start it up 
and the coil was shot.

So my belief is that the Duraspark was driving power into the primary 
side of the coil the whole time the ignition was on.

So this fix would have saved me a coil and I would have been able to 
drive my Pantera to meet Scott Black.

Paul
#9270

Asa Jay Laughton wrote:
> Kirk,
> 
> Great explanation!  It took me a couple of reads, but I got the 
> schematic mapped in my head.  I think it was a very clever way to do 
> it.  Nice work.  I may have to consider this in other projects I have.
> 
> So do you think the coil burn-out was due to removing the resistor, or 
> do you think it would have burned out anyway?
> 
> Asa Jay
> 
> Asa Jay Laughton, MSgt, USAFR, Retired
> 
> & Shelley Marie
> Spokane, WA
> 
> 1973 Pantera L 5533
> [ASASCAT]
>     
> ******************************     
> http://www.asajay.com
> http://www.351c.info
>   
> 
> 
> 
> Kirk Evans wrote:
> 
>>Asa,
>>
>>What happened to me was this---I installed a Duraspark box---wired it 
>>accordingly---started the car and it had no power. I started looking a every 
>>item that could drop power---testing---changing---checking---re-checking---  
>>with no results. During one of the tests, I pulled the resister on the coil 
>>as  directed by the MSD tec guy and 5 to 10 minutes later the coil was 
>>scrap. Put in a new coil and still no power. Then, being totally frustrated, 
>>I, just out of the clear blue, decided to put on an external ground on the 
>>Duraspark box. One alligator ground clip later full engine power was 
>>achieved. No where in any Duraspark diagrams showed the box needing a 
>>chassis ground but in the past, I have always mounted the box direct. This 
>>time to help vibration and backside cooling, I used a MSD rubber mount stud 
>>kit that totally insulated the box.
>>
>>Regardless my fix to prevent a "key on" burn out was this. I put in a relay 
>>with the incoming ignition power feed to the incoming feed on the relay. The 
>>outgoing feed went to the coil and Duraspark box and was also cross 
>>connected to one of the control coil blades on the relay. This will keep the 
>>relay on when it's energized. Along with the back-feed wire on the control 
>>coil, I fed the same terminal with the starter solenoid feed wire from the 
>>ignition. I put on a diode to prevent the starter for being fed by the relay 
>>keeping the solenoid engaged after the key is released. Last the other side 
>>of the relay control coil was grounded. Now when the key is on, no power 
>>goes to the box or coil. Once the started is tripped, the relay energizes 
>>and feeds the ignition accordingly---now the car is running---and the relay 
>>feeds it's control coil from the outgoing terminal. Downside---If the car 
>>stalls, the relay stays engaged until the key is shut off. Once the key is 
>>shut off, the relay dis-engaged no longer powering the coil and Duraspark 
>>until you again trip the key---energizing the ignition parts when needed.
>>
>>This is not a perfect fix but if your working on your car or in the case of 
>>Larry Stock who often has left his key on when loading or un-loading his car 
>>(needing to turn it with the windows down) from a trailer, it will prevent 
>>the burnout problem. There it is---FWIW. The explanation is wordy---let me 
>>know if you need a print. Thanks Asa.
>>
>>Kirk
>>
>>----- Original Message ----- 
>>From: "Asa Jay Laughton" <asajay at asajay.com>
>>To: "Kirk Evans" <kre at adelphia.net>
>>Cc: <detomaso at realbig.com>
>>Sent: Thursday, June 21, 2007 12:28 AM
>>Subject: Re: [DeTomaso] Dura-spark key-on coil burn-up fix
>>
>>
>>  
>>
>>>Well since nobody else replied, I will. :)
>>>
>>>I've been running a Duraspark II system in the Mach I for nearly 20 years, 
>>>with a stock coil.  No problems really.  So my first question is, was this 
>>>due to the coil being an MSD?  If so, why?   Seems to me I've left the key 
>>>on for longer than five minutes before with no ill affects.  I know 
>>>leaving the key on can overheat the coil, yes, but what was so sensitive 
>>>in the MSD that cooked it?
>>>
>>>And yes, I'd be interested in your fix. ;)
>>>
>>>Asa Jay
>>>
>>>Asa Jay Laughton, MSgt, USAFR, Retired
>>>
>>>& Shelley Marie
>>>Spokane, WA
>>>
>>>1973 Pantera L 5533
>>>[ASASCAT]
>>>   ******************************     http://www.asajay.com
>>>http://www.351c.info
>>>
>>>
>>>
>>>Kirk Evans wrote:
>>>    
>>>
>>>>Hi all,
>>>>
>>>>I torched a new MSD coil last week with a Dura Spark box---key left on 
>>>>for 5 minutes---first time ever---my bad. BUT because it happened, I came 
>>>>up with a simple relay fix for those who are interested. Hope it will 
>>>>help a few more Dura Spark users.
>>>>
>>>>Kirk _______________________________________________
>>>>
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>>>>
>>>>      
>>
>>
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