HOTTT!!! coil

[str12-340]

A friend of mine and a FABO member passed away several years ago and periodically I help his widow keep his 67 dart going to take to shows. The car has a 340 with Mopar electronic ignition (distributor and ECU), a round (standard shaped) MSD coil and a 2 connector ballast resistor. This system has been in place for a long time. The car has been sitting for 9 months and she went out to start it up for our club's show this weekend (Mopar Magic in Gig Harbor WA). They started the car up yesterday and it started fine and ran fine for a while, then the ignition cut off. After letting it sit for a few hours, it started right back up again and again died after a few minutes. When checking things they say the coil was firecracker hot and stayed that way for a long time - couldn't touch it a half hour later. The ballast resistor was also hot but it cooled down in 5 minutes.

My guess was a dying ballast resistor and recommended that they try replacing the ballast resistor and the coil since it got so damned hot (with a standard coil). Anybody else have insight into this or suggestions on next steps? I suggested that they replace those things, start the car and have someone keep a hand on the coil to see if it gets hot again.

 

[Dana67Dart]

I'm assuming this is a new issue.

I think for the price of a stock coil it would be the first thing I would swap out

You can measure the positive voltage between the battery negative and coil plus while it is running. It should be in the 6 to 8 volt range at idle and 8 to 10 at a few thousand RPM.

If you are getting full battery voltage to the coil positive, that can and will cook coils unless they are designed for full 12v.

Ballast resisters fail open so not likely the issue UNLESS it is bypassed or the coils that make the resister are somehow shorted in the back.

 

[67Dart273]

I doubt it is the ballast, and agree that the coil is likely going away. The only other possibility I can think of is that they mistakenly left the key in "run" with the engine stopped, and continued to heat the coil

 

[AJ/FormS]

You didn't say where the coil is mounted;
Firecracker-hot? I cannot say, lol.
180* on the back of the intake, could be sortof normal, could be higher.
160 is almost too hot to even touch
140 is about, too hot to hold on to
120 is nice and warm on a winters eve.

I mounted my SuperCoil out on the apron with a ~3ft coilwire, lol.

 

[4spdragtop]

Also make sure to "match" coil and ballast. Lots of ballast resistors all over the place in specs. Closest I've found is SMP RU11 and RU19. Those spec from 0.5-0.7 ohms.

 

[bee1971]

"a round (standard shaped) MSD coil and a 2 connector ballast resistor."

Get rid of the MSD Coil .7 OHMs CDI Ignition Coil

Go with a Standard Motor Products 1.5 OHM Canister Oil Filled and the Matching Resistor mentioned above .5 to .8 OHMs Ballast Resistor