I have a 2000 Mustang GT. As I was driving down the road I smell something burning. By the time I pulled over and got my hood open, my number one coil pack was on fire. Luckily, I was able to get it out fairly quickly. Once I got my car home that night I pulled out the coil pack and there was a big crack on the bottom of it. A few days later I picked up all brand-new spark plugs and a set of eight MSD coil pack blasters and got them all installed. Right as I turn my key and started my car, the same exact coil pack, even though it was brand-new, started crackling and smoking, so I turned off the ignition quick. I pulled it out right after and the spark plug was perfect but the bottom of the brand-new MSD coil was cracked within a matter of 15 seconds.
The ignition coils are only meant to withstand a high electrical charge whereas the spark plugs can withstand that as well as the explosions within the combustion chamber. It is possible that you could have a small crack in your intake manifold or cylinder head allowing combustion chamber temperatures to be exposed to the ignition coil, causing the burning. I would recommend having a professional run a compression test on the cylinder in which this is happening as it is likely the cylinder will not have as much compression with a crack in it.
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