Repeatedly Killing Ignition Coils

[Anonymous]

Hey all,

I have killed 2 ignition coils in the last year. The first one took me a long while to diagnose and the second one never totally died, the resistance changed significantly and I tossed it before it left me stranded. The one I have in now stumbled once and died twice last night. I can't figure out what's causing this. The coil I have in now did the first 20 miles ok but on the way home it died those two times. When I got home I measured the resistance and it was 5.47 Kohms while MSD lists it as 4.7, so the resistance is already changing on the way to ultimate failure.

Are there any "typical culprits" in this type of a situation?

I am running a 200 I6 with points and a ballast resistor hooked up before the + side of the coil. I bypassed the resistor wire. Plugs were recently cleaned and regapped to 0.040.

Any help y'all can give is appreciated.

-Dan

 

[t-west]

I'd like to paraphrase if I might to make sure I understand.

You're running a stock dizzy and coil, which would require you to use the resister wire, but are bypassing the wire. And it sounds like you are also using the MSD to fire the points.

If this is true, I'm guessing that you need to use the resister wire for your coil. Many flamethrowers now sold are for use with the resister wire (see the ohm rating for the coil you're using).

Am I misunderstanding?

--tom

 

[CobraSix]

I think Tom is on to something.

If you are using a stock coil, then you should probably keep the resistor wire in place.

Slade

 

[Anonymous]

Thanks for the help so far, lemme clarify my car's current setup.

When I bought the Falcon I put a Pertronix in it and a new MSD Blaster II coil. The Pertronix wanted a full 12V so I bypassed the pink resistor wire to supply it with the voltage it wanted. I tossed the pertronix some time ago but I am still using an MSD Blaster II coil. The tech on the phone said that the coil works well up to 18 volts. Since I reinstalled the points I have been using the wire that bypasses the pink resistor wire and running it to the ballast resistor that came with the MSD. The +12, then cut down to +6, goes to the coil. - side of the coil goes to the points.

I am not sure that I have ever changed my plug wires but I have tested their resistance and they seem ok. I will get a new set when I eventually change out my distributor to a DSII or one of the new ones Mike is coming out with.

That should clear things up some. Also, the resistance measurement the other day was hot, at the end of the drive. I measured the next day and resistance was down to 4.74 Kohms, which seems to be just about right.

The car has been sitting for a couple months here in Florida with 1/4 tank. The last few times I played with the Falcon it wouldn't start without carb cleaner. When I got it started the first time I filled the gas tank and took it for a drive to charge the battery. Could carb/fuel problems cause random dying of my car as I drive down straight roads? The car restarted immediately, one time it restarted while I was rolling down the road and the other time it restarted onteh first crank after I pulled over.

I definitely did have 2 coils die on me but I might be past that now because I had the ballast resistor on the - side of the coil for a while and I think that was a mistake that killed them. Now I have the ballast resistor on the + side of the coil so I thought I fixed the electrical problem but I can't be sure. I am still getting some infrequent stalling and since I have been having definite electrical problems with those last two coils that is the first culprit that comes to mind. Could the current problems be fuel related?

Thanks, sorry for the long post.

-Dan

 

[CobraSix]

Yes, very likely your problems could be related to fuel. Sometimes you just get bum electronics. I once bought a new voltage regulator only to find out it was bad out of the box.

If you've had fuel sitting for a long time, I'm willing to bet you may have some of the fuel passages in your carburetor that are clogged up some, thus causing random stalls.

Slade

 

[66Sprint6]

I went thru the same problem a while back and someone brought up the fact that the coil is on the motor and that heat was possibly the cause. Im goin to move it to the fenderwell when I get it back just in case. Good luck!
Matt

 

[Anonymous]

Sounds as much like a clogged fuel filter or trash filled carb as anything. mostly clogged filters will often run the carb out of gas when cruising down the road and when you take the load off ,enough gas will get by to get er going again.
---The block may not be the best place for a coil but the one on my 62 lasted decades there. The polarity thing could well have caused your earlier failures- the coil fires when the points open as the points and condenser or the petronix set up is really a controlled short of sorts, the rotor completes the circuit to the plugs -another controlled short-. Thus pumping juice to the ground (-) side of the coil is gonna cause problems--I actually have seen whole wiring harness's go up in smoke when hot wireing to the wrong side of the coil with 12volts. Lots of people at body shops have been fired for that (includeing me when i was 14).

 

[XPC66]

I'd be checking for too much dwell.

 

[Anonymous]

How do I check for dwell? That's just the amount of time that the points are closed right? Do I adjust it by widening/shortening the point gap?

-Dan in Jensen Beach, FL

 

[addo]

You need a dwell function on your test meter. It's a much better method than gapping points with feelers.

Regards, Adam.

 

['61 Draggin Wagon]

My M715('67 military Kaiser-Jeep 5/4 ton pickup truck) puked a coil a couple of years ago after being driven for an hour at highway speeds. I replaced the coil with a new one. About 6 months later the truck started running bad after 45 minutes of driving at highway speeds & quit. Long story short; the condensor, if bad, will kill an ignition coil. Try finding a 24 volt military ignition coil on a Sunday....

 

[XPC66]

How do I check for dwell? That's just the amount of time that the points are closed right? Do I adjust it by widening/shortening the point gap?

-Dan in Jensen Beach, FL

No it's the number of cam degrees the coil is charging (points closed). Too much dwell causes the coil to heat up.

A typical points coil only needs about 80 microseconds to saturate. There are several rules of thumb e.g for a six 360°x0.5/6 = 30° or 360°x0.75/6 = 45°.

If you have a six running at 6000 rpm then six sparks have to occur in 20 milliseconds. That's 12 events (open/close) or 1.67 m/sec per event (30°) , however contact bounce etc will shorten the dwell time markedly. Even so there is a fair amount latent time for the charged coil to sit waiting for the points to open.

If you open the gap you decrease the dwell, but for every degree you decrease dwell you will advance the spark timing two degrees.

Make sure you have a ballast resistor in series with the coil.

 

[mustang6]

Hi Dan,

See my coil for sale in the ads area under http://fordsix.com/forum/viewtopic.php?t=32693

These big coils are designed to run 12V and I've never seen anyone kill one of those.