Coil Fails after several hours of run time.

[scuba scott]

I have a 1981 Mercruiser 470 that runs great with a new coil. The problem is, the coil will fail after several hours of run time. The first two coils I replaced failed, so I installed a "Pertronix Ignitor", electronic ignition module. I replaced the battery wires and checked the ground connection to the back of the block. I use a mercruiser coil. I installed a new altinator. Now what? Could the external resistor be failing. Is there a short that can cause this to happen?<br /><br />Thanks

 

[rbezdon]

Re: Coil Fails after several hours of run time.

simple answer is yes. Original coils are designed to run on 9 or 10 volts. This is so there is spark during cranking when the starter load lowers the battery voltage. Since the battery voltage is 12 volts normally, there is a ballast resistor in series with the coil so that the coil only sees the 9 volts or so during normal run. To get the full battery voltage to the coil during cranking there is a set of connections on the starter solenoid to "short out" this ballast resistor while the starter is engaged. So it is possible for the ballast resistor to be damaged, shorted or some other electrical problem which would apply full battery voltage to the coil all the time and overheat it and cause it to fail. One possible solution would be to install the Pertronics coil which requires a connection to the 12 ignition and forget the ballast resistor. The other option is to of couurse trouble shoot the problem with the resistor.

 

[Laddies]

Re: Coil Fails after several hours of run time.

I have had 2 starter solinoids with the Ign bypass shorted that burned the coils out. can be cked with a volt meter or by disconnecting it temperally

 

[tommays]

Re: Coil Fails after several hours of run time.

if you have the orginal 470 chargeing system they can put out very high voltage if the regulator starts to fail 15 volts or more<br /><br /><br />tommays

 

[Olds Eddie]

Re: Coil Fails after several hours of run time.

I don't know if this is the problem or not but a Pertronics ignition should not be used with a ballast resistor. I'm supprised you even got her started. Get an epoxy filled performance coil like the MSD high vibration coil and pitch the resistor and your problems should be fixed.

 

[prockvoan]

Re: Coil Fails after several hours of run time.

Can ya'll guys put some more light on this ballast resistor?Don't know anything about it.Does TB IV have it in it?Last time I fired up my engines,I had check the voltage to the coils in found that I had 12 volts.Is that what I should have?

 

[Scaaty]

Re: Coil Fails after several hours of run time.

Can of worms here....get the coil that goes with the Pertronix. Call them and explain what you have, and what you might need to do about the ballast resistor elimination (if needed). Some are a ceramic block, or a curly wire, and some coils have them internally. They do this daily, and should get it right for you. Good luck (I HATE electrical problems). Laddie also had a good answer with the starter solenoid

 

[rbezdon]

Re: Coil Fails after several hours of run time.

Olds Eddie, Pertronics needs a ballast resistor in front of the coil IF it is used with the OEM coil. The ballast resistor is a function of what coil you are using, not the module. The power for the module still needs to come from the +12 though. In this configuratikon you are just not getting all of the bang for the buck from the Pertronics. If you change to the better coil, then you can by pass the ballast resistor and get more energy into the ignition.

 

[scuba scott]

Re: Coil Fails after several hours of run time.

Thanks for the advice. I ran the boat yeasterday with the new coil and the engine ran fine. I bypassed the resistor and installed the Pertronix high performance coil.

 

[scottatwork]

Re: Coil Fails after several hours of run time.

My only experience with Ballast resistors comes from a 1979 VW Rabbit.<br /><br />When it goes bad and "Opens", your car will start, and then immediately stop......much like my boat did last weekend (Different problem).....<br /><br /><br />That's a symptom of a ballast resistor being bad....

 

[whywhyzed]

Re: Coil Fails after several hours of run time.

Scott is right, but then what many people do is figure out how to bypass rather than replace the resistor. Then the Rabbit or whatever old car or not so old boat makes it about 5 miles or so before the coil burns up....

 

[scuba scott]

Re: Coil Fails after several hours of run time.

I burned out another coil last weekend. This was a pertronix coil, 40,000 volt with no resistor required. I noticed the Tac. would peg out full when the motor reached about 3000 RPM. My guess is that the Tac wire is shorted somewhere and causing the coil to fail. I removed the Tac wire from the coil, and installed my backup coil. Everything is running fine for now. The motor does run rouge after running hard for 20 minutes. It will cut out and drop 500 RPM's for a minute and then regain strength. The only extra wire to the coil now is the 12 volt bypass. I tried to pull this wire, however it did not want to start. I will check the plugs to see how clean they are tonight.