# What makes a coil pack go bad?



## brian v (Dec 25, 2011)

I asked this question exactly 3 years ago and no 1 has answered IT todate so no some one really knows I guess ..chalk it up to a factory defect I guess .


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## cruzeman48 (Aug 18, 2013)

I guess when I feel it's time to replace it again, I won't go with an ac/delco this time, I will try another brand. There is not much to chose from, but one of them has to be better than the other. I wonder why others haven't had this problem.


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## Merc6 (Jun 8, 2013)

Moisture/corrosion is what claimed my 1st 2.


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## ChevyGuy (Dec 13, 2014)

The only thing I can think of is excessive plug gap. That raises the voltage the coil has to generate and puts more stress on it's internal insulation. I don't know what signals are fed it the coil pack - I suppose it's possible that something is wrong and it's stressing it.


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## cruzeman48 (Aug 18, 2013)

ChevyGuy said:


> The only thing I can think of is excessive plug gap. That raises the voltage the coil has to generate and puts more stress on it's internal insulation. I don't know what signals are fed it the coil pack - I suppose it's possible that something is wrong and it's stressing it.



My gap is at .033 if I remember correctly. I know it is not a moisture problem because I live in one of the driest and hottest states around. Is there a way to test the coil pack?


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## ChevyGuy (Dec 13, 2014)

cruzeman48 said:


> Is there a way to test the coil pack?


Other than swap with a new/known good one? None that I know of. Not without putting the spark plugs into a pressure chamber to simulate boost + compression and see if it can still fire the plug.


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## NickD (Dec 10, 2011)

Was already retired when this thing came out, only thing the shop manual offers for the coil pack is the connector diagram.

View attachment 165538


While I haven't played with it will assume its typical using four autotransformers, a coil with a tap on it. High side would be the point that connects to the spark plug, 12V would be applied to the center tap of all four coils, low side brought out as four individual low side of the coils. 

Would suspect that connecting an ohmmeter to the 12 V input, would measure about 3-4 ohms for each coil input, and around 10K ohms from 12V to each high voltage terminal that contact the plugs. Typically the low side goes to a gated bipolar NPN type of a transistor that pulses each coil in the firing order sequence. When this transistor switches off, the magnetic field collapses rapidly to induce a high voltage in the coil.

Since I have all kinds of electronic test equipment, can test one coil at a time using a spark gap tester at the output.

View attachment 165546


Would expect to see a spark with a 3/8 gap.

In the ECU is a zener diode connected from the collector of that gated bipolar transistor to 12V, if a spark plug is not connected, that diode absorbs the energy, we could never make this large enough to meet cost restrains. One key reason why I gap on the low side. 26 mils for the Cruze, also a much hotter spark and the engine runs far better.

Going back a couple of years when we used a separate ignition module, ha would replace those zeners in my own stuff with larger ones. Not the ignition module is part of the ECU, would do the same thing. 

Ohmmeter only shows continuity, even if the continuity is good, can still have a dreaded just one shorted turn in the coil that eats up all the energy. Yeah, do have a tester for this as well. But seeing that spark proves its okay when bench testing. 

It was late on a Thursday night we picked up our new Cruze after listening to all that BS about OnStar, XM, and extended warranties on our brand new 2012 2LT. But quickly noticed when we finally got free of all that BS with a hundred of no replies, if I eased the clutch out in first gear, the engine would kill. This is no good.

Next morning pulled the plugs, did not like those needle point NGK's, can't carry the heat, so put in Autolite APP3923's gapped at 26 mils. Also noticed when I pulled the coil module, those springs were hung up in the booths. This is dumb, so stretched them out so they won't hang out. When I install the coil module, hold it at an angle so I can see contact with all four plugs with those springs. What a difference, can even ease out the clutch in 3rd gear without killing the engine.

Wanted to also grease the battery terminals with dielectric grease, found the negative battery terminal loose with a tight screw. Removed that and filed a gap so it would be tight. Not only that terminal, but all the positive ones, kind of dumb to put all those terminals so close to that battery acid. Call this post production work.

Three days later my coolant reservoir was low, just figured they left air pockets in, typical ever since they dumped that radiator cap. Already had a bottle of Dex-Cool, topped it off, hasn't used a drop since.

Last job for that day was installing my own mud flaps, got screwed from my dealer on my 04 Cavalier when new, did a terrible job with sheet metal screw in an 1/8" thick plastic wheel well and were on crooked. Used plastic push pin rivets instead. While I was at it, anti-seized the rotor hubs, if you don't, with road salt, can't even remove a tire because it rusted on so bad.


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## obermd (Mar 3, 2012)

What plugs are you using? It's possible your gap has grown and is now causing issues. I know my ECO MT starts having issues when the gap on any plug exceeds 0.037" Other than corrosion, a torn boot, damage to the plug, or other physical damage there really isn't a lot that can go wrong with our coil packs - it's a pretty stupid simple circuit encased in a shell of plastic.


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## NickD (Dec 10, 2011)

Would ever think dirty contacts on my ignition relay would cause my radio to flash on and off. But was the first thing I checked, since it fires the ECU that talks to the BCM. Been a week now, and radio has been working perfectly. Really loading those tiny little contacts with four fused circuits. May also be your problem.

Coil module harness wraps around and heads directly toward the ECU mounted on a plate smack next to the battery. Whenever GM even ran a cable harness near the battery, battery acid would drip on it causing problems. Have to keep your battery perfectly clean to prevent this, those coil wires go into one of those three connectors, corrosion can also be the problem. 

A lot of times a victim customer has to lay out $$$$ for a new ECU, when the only difference between the new and old one, is the new one has clean terminals. A lot cheaper to clean them.


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## cruzeman48 (Aug 18, 2013)

Thanks everyone for their thoughts and suggestions. I am running the NGK plugs. I will have to check the gap on them again. I will also be checking the wiring harness and connection and the battery connections.


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## ChevyGuy (Dec 13, 2014)

I imagine there are tests that could prove a coil back is bad, but I'm not sure as there are any that can prove it's good. You could have a partially shorted coil, or a break down in the insulation that prevents it from having enough voltage to fire a large-gap plug with full boost. Because of the way the coil is integrated, there's no place to put a current clamp on to see if there's a spark with it in the engine.


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## Merc6 (Jun 8, 2013)

With mine it was obvious both times besides a dead cylinder. Gaps on the plugs were 0.027 for the BKR7EIX


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## newsguy99 (May 24, 2013)

I would look up in the boot, and see if the spring is not stuck on the side of the boot.


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