Is it normal for Coils to get very hot? - Defender Source
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  #1  
Old August 8th, 2006, 07:17 AM
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Bryan Tate
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Is it normal for Coils to get very hot?

I had my mechanic install a Mallory Distributor and the MSD blaster high vibration coil. (94 d90)
Anyway, the coil is getting very hot (my mechanic called and is concerned)
Is that normal or is there a problem with the wiring/coil?

Thanks
Bryan
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  #2  
Old August 8th, 2006, 10:13 AM
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Robert Dassler
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There are a couple types of coils, resistor & non-resistor. If the MSD coil is a non resistor type you will need to put a ballast resistor inline on the primary side or it will overheat.
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  #3  
Old August 8th, 2006, 10:32 AM
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Bryan Tate
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It does have the ballast resistor (I assume its inline)
It also is getting hot, which I understand to be normal

The mechanic said it gets so hot he can't touch it after 2 minutes
He put my old coil back on and it gets just as hot.......I'm calling Mallory to see what they say

Thanks
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  #4  
Old August 10th, 2006, 11:14 AM
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Heath Ahrens
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Any word??? I have the same setup and my ignition stutters when cruising at relativley low rpms. Either the plug wires, plugs or coil. I need to check if mine gets hot and I will let you know.
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Old August 10th, 2006, 12:40 PM
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Chris Davis
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I run the mallory and the stock coil and a ballast resistor(Mallory). Mine runs perfect, does not run hot.
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  #6  
Old August 10th, 2006, 01:37 PM
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Bryan Tate
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Ok,
I called Mallory, they strongly recomended not using the MSD blaster with the Mallory

I ordered the Mallory coil with internal resisitor and it seems to be running fine!!
They don't know why, but they said they aren't compatible and it can melt the MSD coils
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  #7  
Old August 10th, 2006, 02:31 PM
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Chris Davis
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Bryan, which Mallory coil did you go with?
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  #8  
Old August 10th, 2006, 04:59 PM
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Huh... That is wierd... I have a resistor in line also with the msd high vibration coil...
I was using an old coil out of a chevy small block 350... I should not have "fixed it" since it worked fine.
I am putting the old one back and see how it works.
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  #9  
Old August 10th, 2006, 05:16 PM
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Matt Hurst
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i have the mallory with the msd blaster coil and an inline ballast and its fine. i had the mallory with the mallory coil with internal ballast and it cooked the coil and it exploded.
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  #10  
Old August 10th, 2006, 07:28 PM
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Maybe coils in general are often defective??? I cooked the stock Bosch (silver outside) which looked like a good unit when I installed the Mallory distributor. The guy from Mallory told me the rover Bosch coils are crap. It made a huge mess on the inside of my fender... like molten black plastic poop that won't come off.
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  #11  
Old August 23rd, 2007, 10:22 AM
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Sorry for reviving such an old thread, but this one most closely resembles the problem on which I wanted to poll this board.

Scenario: 1995 ST with the stock 3.9. When I bought the truck, it was running very erratically. A local shop determined the stock distributor was wiped out, so I replaced it with a Mallory 8901 and a Mallory 29219 coil (thanks to suggestions from this board!) Before I ordered this setup, I was advised (by whom, I can't recall) that I did NOT need the Mallory 700 ballast resistor, because I was using the stated coil with a Unilite (now "e-spark") distributor. Also, I checked on Mallory's knowledge base, and it confirmed that a ballast resistor is not needed with an 8901 dizzy and a 29219 coil.

Well, the other day, I was under the hood, and I noticed that my coil was hot. I mean HOT. I mean REALLY HOT! (At the time, I wondered that, if I closed the hood, I might be able to see it glowing!) Knowing this COULDN'T be right, I contacted Mallory to ask about it. The first tech I reached told me to do three things:
1. Check to see if you're getting 12V to the positive side of the coil (I'm getting 11.19V)
2. Check the resistance across the terminals of the coil, and you should get 1.4 ohms, +/- 10% (I could get no reading at all)
3. Check the resistance from the positive side of the coil to the coil tower, and you should get 10K ohms, +/- 10%. (Again, I could get no reading there either)

I called Mallory back, and the second tech I reached said that 11.19V to the coil was fine and that I needed to use the ballast resistor. When I told him I had been advised not to use it and that their knowledge base confirmed that, he said I shoould use it anyway.

Bottom line: I know virtually nothing about auto electrics. Furthermore, I don't know what bad (or good) adding the ballast resistor would do. Therefore, can anyone on here advise me on whether or not adding the resistor will cause any harm? I don't know whether the proper advice is "you can use it, but you don't need it" or "you shouldn't use it on that application." Anyone have any recommendations?
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  #12  
Old August 23rd, 2007, 05:56 PM
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Jim Ngo
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This is a similar problem I had. I replaced my distributor with a Mallory Unilite and was also told I didn't need a ballast resistor as there was one inline.

WRONG. And there are 2 good reasons why.

First of all, there isn't any inline ballast resistor that I can see physically, or have seen in any wiring diagram for the D90.

Second, some say that there is an internal ballast resistor inside the stock coil (I don't think the one that was in the D90 when I bought it was stock though). Even if the stock coil has one, the coil is protected but it wouldn't help protect the Mallory's 'e-Spark' ignition amplifier, which is about a $100 part. If the ignition amplifier is getting full current then it will die, probably soon.

The reason why I know this is because my coil eventually blew and I had to replace it AND the e-Spark module, along with a melted rotor and distributor cap. I now have an inline ballast resistor. Check your Mallory Unilite installation instructions. It states very clearly that you need to make sure there is one installed. I learned that lesson the hard way.

Having too much resistance to the coil MAY cause missed ignition spark. If that happens then you can lower the ballast resistance. I went with 1.4 Ohms and it has been fine (knock on wood).
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  #13  
Old August 24th, 2007, 06:11 AM
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Quote:
Originally Posted by Heath
Any word??? I have the same setup and my ignition stutters when cruising at relativley low rpms. Either the plug wires, plugs or coil. I need to check if mine gets hot and I will let you know.
The ECU gets its signal from the coil. When running a "hot" coil there is enough resistance to effect the signal to the ECU and cause the "stutter". You need to signal the ECU through a seperate electronic tach drive or go back to a stock (or similar) coil. Unless you are running an extremely modified motor, that revs to over 6000 rpm there is no need for anything other than a stock coil....other than the "look" I suppose.
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  #14  
Old August 26th, 2007, 11:03 PM
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David
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Just a follow up on my coil cool down: I followed the latest Mallory tech's recommendation (not their written suggestions or guidelines on their knowledge base) and installed a Mallory 700 ballast resistor. All is now good! Though the coil gets warm-to-hot, it's not hot enough that you can't touch it like before. It gets plenty warm, but not glowing hot.

Anyway, now I have another question: is it possible that adding a ballast resistor could make my truck run......BETTER? I'm not sure there's any rationale for this, but I swear it seems to run smoother! This could all be in my head, but when I first drove it, it was conspicuously smoother.........anyone have any thoughts (an explanation of what could have been helped or an explanation on whay I'm crazy)

As always, thanks for all the help...............
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