Coil pack keeps failing

Hi all, wonder if anyone can shed any light or ideas on an ongoing issue.

Some time ago my sister, who has a 2007 Jimny rang and said she had a misfire.
I said it could be a coil pack, sent her a link and her partner replaced it, which seemed to cure it.
A few weeks later she got in touch to say she had been on the motorway and it had happened again, the car had lost power with a misfire, and she called the AA.
The AA said the coil she had fitted was no good, and had fitted a hella coil (or maybe fitted two - I can't remember)
Again this fixed it and we thought maybe the coil off amazon wasn't so good.
She went on the motorway again, and said it had happened again, so I told her to come over and we'd have a look and try figure it out.
I got a cam sensor, and a crank sensor, fitted them, and put ANOTHER coil on.
This seemed to cure it, and she went again onto the motorway, and the coil didn't just fail, it literally melted!!!
We were a little stumped, so we tested the resistance of the HT leads and one seemed normal, and the other way out.
So I put new HT leads on, and drove it a few junctions down the motorway and back, and the coil was hot but nothing excessive.
She drove it locally for about 200 miles, locally as she was a bit wary, then when she felt confident she went onto the motorway and the symptoms happened again.
The coil sounds like it has failed again (I haven't seen it yet) but, someone put a code reader onto it, and it show a crankshaft sensor as a fault.

Anyone have any knowledge or ideas on what could be causing this, or how to cure it?
It's difficult to fix, as it seems to only happen after prolonged high revs, which sounds like it's asking for a lot of spark, for a long time.
So even if we fit anything new, unless we drive it prolonged down the motorway we won't know if it's cured - unless there is a better way?
Is this symptomatic of a faulty crank sensor?
Could the new crankshaft sensor we fitted have been faulty out of the box maybe?

One more thing, the idle is just a little lower than it should be - it sits around 500/550 - I have taken off the throttle body and cleaned the ICV.

Thanks for any help.
 

The easiest thing to check is the spark plugs, when they wear the gap gets bigger and the coil works harder, I've never seen one melt a coil pack though, they normally break down the coil insulation (and if if says Ford on the boot lid damage the ECU).


If it is crankshaft sensor the engine just cuts out when hot and the rev counter drops to zero. It doesn't usually cause a missfire.


 

Thanks - she put a new set of Bosch spark plugs in, but to be on the safe side I swapped my iridium ones out of mine into hers.
We're not sure if there is anything left on the ignition system - apart from the ECU which is very last on the list of possibilities..

The ECU just sends a control signal to the coils, the current switching is done by electronics inside the coil, so I wouldn't have thought the ECU would be faulty, more likely the coils or the wiring connections/insulation.


You'll have to 'scope the signals to the coils when the engine is fine, and then again when it is missfiring and see if there is a difference, the ECU is coded so you can't just swap it out with a spare for a quick test.