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 Post subject: BOOM! goes the coil
PostPosted: Fri Sep 20, 2019 12:50 am 
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TBI Slant 6

Joined: Tue Apr 05, 2011 11:34 am
Posts: 107
Car Model*:
Here we go! I just changed my `65 Valiant Convertible over to a MoPar electronic ignition. I did this a couple of years ago with a `62 Valiant with great success, so I was rudely surprised by this project. Here is the story:

I've had this car forever and the `76 engine I have been running for 30 years finally needed to be torn down so, instead, I tore down a seedy looking `67 block that I bought for $50. After boring it .040 over and replacing everything in it but the piston rods, we were ready to start the baby.

The good news is, it runs just great. The problem has been with the electrical system which is now modified with extra leads for the ECM and distributor, which I scored off a wreck at the junk yard. So, some of the wiring is from the donor car and some of it is stock. I paid special attention to how the coil is wired up, using several wiring diagrams for both the old and new setup as references. Everything seems to be fine and, as I noted, it runs like a dream...

For about 15 minutes...

...Until the coil exploded.

Fortunately, nobody was near the car when, without warning, a *POOF* came from the right side of the engine, and a jet of boiling hot oil shot 5 feet over the car. The hood is off, so it was pretty dramatic looking and I am real glad I didn't get it in the face. The coil had overheated so badly that the oil inside expanded to the point of blowing the plastic top free of the flange, and partially ejecting the rubber "O" ring that seals it. The coil was so hot that, one hour later, it was still too hot to touch. Remarkably, the engine stayed running. I had to shut it down.

OK, so I look this problem up and see that some of you have had that happen to you. I read about the 3 ohm Pertronix coil being able to be used without a resistor so I figure even if I totally botched the wiring, if it doesn't need a ballast. It's bulletproof.

I have a 3 ohm Pertronix on the shelf, so in it goes. I disconnected the remains of the coil and the solenoid lead to the starter and turned the key to "RUN."

I then took readings at every point of the system that I could think of. In the 25 minutes it took to take these readings below, the Pertronix coil got pretty warm, *almost* too hot to touch.

Most of these are taken with the switch in "run" mode, except the Battery Terminals, which was taken with the cables disconnected and the meter stright across the battery. The readings taken in "start" mode were taken with the solenoid wire disconnected, as noted above. The starter relay engaged as normal.



Battery Terminals............... 11.96
+ of Batt to M/C bail ground: 11.92
Ballast Blue side........... 10.55
Ign #2 at resistor ......... 10.36 Run
Ign #2 at resistor........... 10.03 Start
Coil + .............. 10.35 Run
Coil + .............. 9.55 Start
Coil - .............. 1.274 Run
Coil - .............. 1.171 Start
Pin #1 of ECM..... 10.93
Pin #2 of ECM..... 10.93
Pin #3 of ECM..... (not used) 10.94
Pin #4 of ECM - black dist. lead . 00
Pin #5 of ECM - orange dist lead .00

All measurements use the Master Cylinder bail as ground. This was for convenience, as it was very easy to get the test probe to stay stuck under it.

For reference, I tested a few other ground points with similar results. For instance, the coil + measurement was one one hundreth of a volt higher when using an engine ground for the meter.

Now the questions:

- How can I be cooking coils with a mere 10.5 volts?

- Would sitting with the key on with the engine not running make the coil hot?

- Where is the voltage drop going across the resistor? No matter what position the key is in, the voltage only shifts by about .3 volts, and it goes the wrong way. It drops.

By the way, speaking of the resistor, I checked the resistance and found one side to be about 1.6 ohms and the other side to be around 6 ohms. I'm not sure what the 6 ohm side even does. It has a green with a red trace wire that goes to pin #3 of the ECM plug, which has no mating pin and is, essentially, a dead end.

_________________
1961, 1962, 1963 and 1965 Valiant 200. The `65 is a `vert.


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 Post subject: Re: BOOM! goes the coil
PostPosted: Fri Sep 20, 2019 4:23 am 
Online
Turbo EFI
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Joined: Mon Jan 12, 2015 5:55 am
Posts: 1059
Location: Brightwood, VA
Car Model*: 1965 Plymouth Belvedere I
There was a change made to a 4 pin module. It looks exactly like the 5 pin module and is a direct replacement for the 5 pin module. It basically eliminates the 6 ohm side of the 4 pin resistor. If the key is in run, and current is flowing, I don't think it unusual for the coil, and other electrical devices (module) to grow warm, especially if no air is flowing (engine fan).

_________________
-MattMan
Strive for Excellence, not Perfection.
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 Post subject: Re: BOOM! goes the coil
PostPosted: Fri Sep 20, 2019 5:34 am 
Offline
TBI Slant 6

Joined: Thu Apr 18, 2019 7:57 am
Posts: 131
Location: Lawrenceville, GA
Car Model*: 1966 Dodge Dart
Badvert65 wrote:
If the key is in run, and current is flowing, I don't think it unusual for the coil, and other electrical devices (module) to grow warm, especially if no air is flowing (engine fan).


Current shouldn't be flowing through the coil with the key on and engine off with an electric ignition module, however. This sounds like either a failed ignition module or a wiring problem. The negative terminal of the coil should read the same voltage as the positive in key-on, engine-off state.

Note - see below, looks like I had missed a quirk of the Chrysler modules.

_________________
Matt Cramer
1966 Dodge Dart turbo / EFI project


Last edited by MadScientistMatt on Fri Sep 20, 2019 11:29 am, edited 1 time in total.

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 Post subject: Re: BOOM! goes the coil
PostPosted: Fri Sep 20, 2019 6:40 am 
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2 BBL ''SuperSix''
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Joined: Thu Aug 29, 2019 8:42 am
Posts: 12
Location: Decatur, Illinois
Car Model*: 1970 Plymouth GTX
MadScientistMatt wrote:
Badvert65 wrote:
If the key is in run, and current is flowing, I don't think it unusual for the coil, and other electrical devices (module) to grow warm, especially if no air is flowing (engine fan).


Current shouldn't be flowing through the coil with the key on and engine off with an electric ignition module, however. This sounds like either a failed ignition module or a wiring problem. The negative terminal of the coil should read the same voltage as the positive in key-on, engine-off state.


FYI...
On the Mopar control module (orange box) the transistor on the outside of the heat sink is an MPN transistor that is ON (current flowing) when the ignition is on. When the engine is started/running the pick up coil in the distributor generates a pulse and thru the electronics in the orange box, is amplified and causes the NPN transistor to turn OFF, which in turn, allows the coil to create the spark. If the ignition switch is left on, the current (heating) thru the coil is limited by the ballast resistor and the coil's primary resistance and the transistor's collector-emitter junction resistance. Ttue, air flow in the engine compartment helps to temps to a safe value. Just my opinion of course.
BOB RENTON


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 Post subject: Re: BOOM! goes the coil
PostPosted: Fri Sep 20, 2019 11:28 am 
Offline
TBI Slant 6

Joined: Thu Apr 18, 2019 7:57 am
Posts: 131
Location: Lawrenceville, GA
Car Model*: 1966 Dodge Dart
Interesting. That's about the opposite behavior of virtually every ignition module made after the Chrysler design - I suppose they were just getting started figuring out electronic controls then. I knew Chrysler's design was one of the few that needed a ballast resistor, but I figured it simply had something like a 50% square wave dwell.

_________________
Matt Cramer
1966 Dodge Dart turbo / EFI project


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 Post subject: Re: BOOM! goes the coil
PostPosted: Fri Sep 20, 2019 5:39 pm 
Offline
TBI Slant 6

Joined: Tue Apr 05, 2011 11:34 am
Posts: 107
Car Model*:
Thanks for your thoughtful replies. I knew I would get good advice here.

I guess the next step is to try another ECM and see if that helps. Something made that coil melt down and I am pretty sure my wiring is OK.

I will check back in over the weekend, so if anyone else has any thoughts on this, I welcome them.

In any case, I will let you all know how this turns out. Lets hope I don't roast another expensive coil in the process!

_________________
1961, 1962, 1963 and 1965 Valiant 200. The `65 is a `vert.


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 Post subject: Re: BOOM! goes the coil
PostPosted: Sat Sep 21, 2019 12:20 pm 
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Supercharged
User avatar

Joined: Thu Jan 27, 2005 8:32 pm
Posts: 7603
Location: SW Washington
Car Model*: 1965 Plymouth Barracuda, 1954 Dodge C1-B8
If you have a dwell meter you can check the coil dwell that the ignition box is delivering. OE Chrysler stuff has fixed dwell and controls the current with the ballast resistor. GM HEI controls the coil current with variable dwell which is far superior. The Standard LX101 module was a good part, but since the manufacturing moved overseas I've used HEI retrofits.

_________________
Joshua


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 Post subject: Re: BOOM! goes the coil
PostPosted: Mon Sep 23, 2019 12:59 am 
Offline
TBI Slant 6

Joined: Tue Apr 05, 2011 11:34 am
Posts: 107
Car Model*:
Well, if you guessed a wiring mistake, you had the right answer.

I dug into it again this weekend and determined that the coil wire, which was part of the original harness, was somehow shorted to the run side of the ignition system, effectively bypassing the resistor and delivering full power to the coil.

I solved this by running my own wire from the resistor to the coil and cutting the old harness out of the system altogether.

It now shows about 9.1 volts at the + side of the coil with the engine running normally. Yay for fixed! Now I move on to neatening things up.

Thanks to all of you for your input.

_________________
1961, 1962, 1963 and 1965 Valiant 200. The `65 is a `vert.


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