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Discussion Starter #1
I have a 2013 JK with 3.6 pentastar that blew the #4 coil pack. It was replaced and all spark plugs on that bank were also replaced. Car drove fine for about 15 minutes before it blew the same coil pack again.
I replaced it again and checked the wiring loom for any obvious issues and also cleaned all the grounds. #4 coil pack blew again.
Coil and PCM was replaced, car drove fine again for 15 minutes of driving and it blew the #4 coil pack yet again.
Really stumped with this one. Going to have a better look at the loom but is there anything else that could cause the same coil pack to fail?
 

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Are you replacing the coil packs with aftermarket or genuine OEM Mopar?
What are the symptoms when the coil packs fail?
Do you have the correct spark plugs installed and gapped to spec.?
Did you scan the PCM for trouble codes?

One thing that comes to mind is an open or out of spec. high impedance at the coil pack's 2ndary high voltage output winding.
That would cause the coil to over voltage itself when it fires possibly causing internal arcing in the coil pack.
If the spark plugs are gapped correctly then not sure if that engine uses spark plug wires but if it does, i'd replace them.

Also, there could be for some reason a hot spot in the coil pack's area overheating it.
You could check for that easily with an infrared temperature gun.

Other than that, yeah check the wire harness closely for frayed insulation and any wires shorting to each other, to ground or to B+.
 

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Discussion Starter #3
Ive replaced with both OEM and aftermarket coil packs. The coil packs crack and melt. All spark plugs were replaced after the first coil blew and were gapped. PCM only has codes once the coil pack fails.
Its not the coil, spark plug or PCM. That pretty much just leaves wires and ground i believe.
 

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Coils are fed 12v via a relay and the pcm controls the ground. It sounds like the coil on that cylinder is putting out its max voltage all the time causing it to overheat. I wonder if that cylinder is running lean which could be a cause. Personally I think it needs to be looked at more thoroughly rather than throwing more parts at it because there's more going on there.
 

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Discussion Starter #5
I checked the resistance of the wiring to that coil and im getting 12 ohms. So somethings not right.
 

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Discussion Starter #6
Not sure what i was doing wrong earlier but rechecked all the wiring and all the connections seem ok, <0.5ohms.
 

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Coils are fed 12v via a relay and the pcm controls the ground. It sounds like the coil on that cylinder is putting out its max voltage all the time causing it to overheat. I wonder if that cylinder is running lean which could be a cause. Personally I think it needs to be looked at more thoroughly rather than throwing more parts at it because there's more going on there.
Good theory in that scenario and would likey fry the coil pack.
Whats puzzling though is that the car rides fine for 15 minutes before the packs fail.
I'd think if that was the case there would be misfires on that cylinder, a rough idle or drive ability symptoms for those 15 minutes.

Do any of those CEL codes indicate a misfire on that cylinder?

One possible out there explanation is that the original pack failed short circuit which overheated its control wire thus melting the wire's insulation enough to short the wire to ground only when the engine gets hot.
I had that exact same thing happen with my old '94 XJ's injector harness only two injector wires shorted together.

Barring the unavailability of an oscilloscope and If this were my deal i would compare the control wiring voltage with another pack. I'd do this first with engine off-ignition on then with the engine idling.
Keep in mind the control wire will have voltage pulses so i'd try using both the AC and DC settings on the voltmeter during the comparison.
Or when the pack finally fails, quickly compare ALL of the primary wire voltages with another coil pack.

In any case, i think you're likely right and my guess also is that pack's harness has an issue.
If you had an infrared temperature gun and if indeed a wire was shorting to ground it 'could' produce a localized heat in the area of the short circuit. Again I'd try this first with engine off-ignition on and engine idling.
You can get one of those guns cheap at HF tools.

At any rate keep us updated as this is an interesting problem.
 

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Discussion Starter #8
I get a CEL code for misfire on that cylinder but im sure that occurs when the coil pack fails. No signs of misfire before it fails. Its hard to test wires at the point of failure because i need to remove the intake manifold just to get to the coil connector.
 

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If 100% you're sure the misfire CEL occurs after the 15 minutes of so called good run time when the pack fails its got to be a wiring issue or worse a PCM issue but at this point i kind of doubt that.

Far as removing the intake manifold, there's got to be some other areas to prob the wiring with a voltmeter.
Might need a detailed schematic if you already don't have one.

If the intake manifold is that close to the area of concern thats where i'd first start looking first for anything out of the ordinary.
I really need to take a good look at my V6 tomorrow which i haven't done since no issues still under the B to Ber power train warranty and see what you're seeing.
To be continued!
 

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Discussion Starter #10
After tracing all the wiring, loom looks in good condition. Where the engine loom connects to injector harness, 1 wire has been rubbing the metal heater hose. This 1 wire just happens to be the #4 coil trigger, however insulation is still intact. I have wrapped in electrical tape and then cloth tape anyway to stop any further rubbing. I also swapped spark plugs with another from the other bank just in case replacement was faulty. I have just taken it for a 5 minute drive around the block and all coils are the same temp, no CEL and im monitoring the fuel trims on both banks, all normal. I might get a bit more adventurous later and take it for a longer drive.
 

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Hope that wire rubbing against the heater hose solves the issue once and for all.
Good reference basis point in that all the coils are the same temp.

Another wild arse theory based on whats been said is that there could be an un-observable tiny pin hole in the insulation where the high voltage inductive arc generated from the primary coul could penetrate ground out to that metal hose.

Good luck and let us know if this is the final fix or a fail.
 

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Discussion Starter #12
There shouldnt be high voltage on the primary circuit though right? #4 trigger wire is just a grounding 12v, i was under the impression that high voltage was contained within the secondary circuit.
 

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I shouldn't of mentioned a high voltage spike that could be produced in the primary as i think it added an unnecessary confusion factor.

If the primary's trigger is a ground pulse then there needs to be 12 Volts at the opposite end of the coil's winding.
Once that trigger pulse is initiated a magnetic field is produced in the primary winding.
That magnetic field is coupled or induced into the 2ndary high voltage winding which because it has much much more windings than the primary coil it produces the high voltage (but lower current) spike the spark plug needs.
Basic transformer theory 101.

But if you're interested in what i meant and i'll try to make it basic, read on...if not skip below.
If we replace the PCM's trigger pulse with a simple SPST switch which is then quickly closed it allows an instantaneous current flow through the coil winding which will produce a magnetic field around the coil known as Faraday's Law.

Now when the switch is opened that magnetic field has to go somewhere.
Where? Most of it collapses back into the coil which will generate a voltage spike across the coil which is known as an inductive arc.
The amplitude of that inductive arc voltage spike is loosely proportional to the rate of change of current in the coil, coil winding, circuit load, coil inductance, etc.

The peak voltage of an Inductive arc spike depends on many circuit factors and in some cases can theoretically be up to infinite volts depending on many ciruit parameters.
In heavy industry, automotive electronics, etc. where inductive loads are involved there are precautions to prevent the inductive arcs from feeding back into and damaging other electronic components
If you ever opened a switch in the dark say to turn off a motor, sometimes an electrical flash can be seen in the switch.
Thats the inductive arc in action.

One common example of protection from these arcs is that many relays have a diode placed across its energizing relay coil.
The diode's polarity in the circuit is reversed biased under normal operating conditions meaning it has a very high impedance.
When there is an inductive arc present, the arc's polarity causes the diode to be forward biased meaning it now has a very low impedance which has the effect of shunting the arc's voltage thus protecting any back circuitry components.

Its all a little more complicated but i hope this makes at least some sense that is if you read all of that gobbly ****.
 
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Discussion Starter #14
I taped up the wire where it was rubbing and then put some cloth tape over the top. Cautiously drove around for an hour today and so far so good. I still cant believe 12v was shorting through the insulation enough that it caused the coil to overheat.
 

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I taped up the wire where it was rubbing and then put some cloth tape over the top. Cautiously drove around for an hour today and so far so good. I still cant believe 12v was shorting through the insulation enough that it caused the coil to overheat.
Any chance you could take a picture of the failure point where it was rubbing? just interested to see.
 

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I taped up the wire where it was rubbing and then put some cloth tape over the top. Cautiously drove around for an hour today and so far so good. I still cant believe 12v was shorting through the insulation enough that it caused the coil to overheat.
So far so good. Keep your fingers crossed.
Thanks for the update.
 

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Here's my two cents . . .

Each cylinder has its own high voltage igniter circuit mounted atop its spark plug.

Each igniter circuit is powered up by the same common 12 volt supply and ground.

Then each igniter circuit is triggered by its own individual TRIAC device remotely located in the ignition control module.

Since the TRIACs are controlled by a microprocessor its important that the
HIGH FREQUENCY OSCILLATIONS, (that's in the radio frequency range), required to generate the HIGH VOLTAGE/SECONDARY SPARK PLUG VOLTAGE don't "reflect" back into the microprocessor circuitry, in turn causing malfunction and/or in your case igniter self-destruction.

It seems that the igniter modules "bleed" a degree of this HIGH VOLTAGE OSCILLATION energy back into the 12 volt supply and control wiring.

Its possible that FILTER CAPACITORS within the ignition control module have become weak and are no longer effective at protecting the microprocessor circuitry as designed.

You may want to be on the look-out for a compatable replacement IGNITION CONTROL MODULE thats as new as possible.

Given this senerio, that's what I would do.
 
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