The coil on my Mk2 is knackered me thinks.
Out the other day, all fine apart from a hesitation to rev above 2500, then after about 15 min it started to lose power and misfire, managed to get her home.
Checked over the carbs etc all seemed good so went back out today, same thing happened, does not want to rev above 2500 starts to miss and hesitate then a couple of miles down the road it gradually starts missing until undriveable.
So we poured 3 litres of cold water over the very very hot coil she then started and didn't miss a beat on way home which was only about 10 min away, didn't get chance to test high rev issue but me thinks that the coil is breaking down and needs changing.
Now the coil is only 7 months old from Aldon automotive and is one of there Flamethrower coils product number 40611 a Epoxy filled non-ballast type, purchased along with a modified electronic distributor.
Thing is when I check the voltage across the coil with the Ign on it was only 9.3 volts, please correct me if I am wrong but is that right or should I have a Ballast type coil ??
Many thanks all.

 

Measuring voltage across the negative and positive terminal of the coil with the key ON, doesn't tell you much.
It's showing 9.3 volts because you're including the resistance across the primary windings.

Jaguar's don't have a ballast resistor, so you should be using a 3 ohm coil _ one that does not use a ballast resistor, so it sounds like you have the right one.
To test this, disconnect one side of the coil, it doesn't matter which, and measure the resistance across the negative and positive terminals, it should be at around 3 ohms.
A coil that requires a ballast resistor will measure at around 1.5 ohms.

To test if it's getting the correct voltage from the ignition, disconnect the wire from the coil that comes from the ignition.
The wire from the ignition should be battery voltage with the key on.
One side of your volt meter should be connected to the ignition wire and the other side to ground.
If the car is positive ground, the red wire from you multi meter will be connected to ground and the black wire to the ignition wire.
With a modern multi meters it almost doesn't matter in this case, connecting it wrong will simply show a negative sign on the display showing that your have connected the polarity wrong, but it will still show battery voltage.

What sort of electronic module do you have in your distributor, matching the wrong coil can and will cause failure ?

Know too that Jaguar placed the coil in one of the worst possible locations, right above the rad where all the heat is, moving the coil to the inner fender well closest to the distributor can help.
It's also possible that the coil was and is faulty.

Personally I would use one of the Bosch epoxy coils, the problem is finding one that isn't a knock-off.
You can use an oil filled one, but they must be kept up right.

Here's some info on that:
http://www.ratwell.com/technical/BlueCoil.html

 

Thanks for this JeffR1 will test again as per your directions tomorrow but 99% sure that I have the correct type of coil, just needs replacing and have been advised to go down the Bosch route and relocate if pos like you suggest.

 

Problematic coils usually test fine when cold, sometimes replacement is the only route, and yes, the Pertronix web site shows it as being a 3 ohm coil.
I'm curious, does it say where it's made, it's supposed to be made in the US ?
Maybe they're sourcing there copper wire from China and the varnish on it may be thin.
When coils get hot 2 things happen, the resistance climbs to the point where it no longer fires and/or the varnish breaks down causing internal shorts.
When it cools down, it works fine.

 

Ok, Changed coil to new Bosch Non balllast type and moved position to inner wing between rad and brake fluid reservoir but now car won't start and not getting a spark at plugs.
Have fuel at carbs, pump working, HT lead from coil to distributor good, Ignition live and feed to electronic distributor going to + terminal on coil and then - terminal has another cable to distributor and cable going to rev counter I think.
Battery good, engine turns over ok but won't fire up, does anybody have any ideas, supposed to be taking her to the Silverstone classic tomorrow........

Thanks

 

Also when I put the old coil back on it still wont start....

 

The rev counter on a Jaguar is totally separate from the ignition, so I'm not sure what black wire you're referring to and where it goes.
The rev counter on a Jag is driven off of a small DC generator at the back on the intake cam _ unless someone has changed yours.

To help you further I need to know what aftermarket ignition is in your distributor, but from the sounds of it, it looks like the electronic ignition has failed since now it will not run with the original coil.

The other thing that concerns me is if your car is negative or positive ground.
To check this, look at the batteries terminals, if the + side of the battery is connected to the firewall, then it's positive ground, if the - side of the battery is connected to the fire wall, it's negative ground.

If the car is wired for positive ground, then you may have connected things wrong, but it may have been changed, even more so if someone has installed an alternator.

Here's a video on how to bench test the coil itself and bypass the electronic ignition, it's not the greatest, but hopefully it will be enough.
With that said, it's unlikely both coils are bad, that's why now I suspect the ignition module has failed or things are hooked up wrong, but I can't really help you there until I know if the car is positive or negative ground and what make the ignition is.

EDIT:
Know too that if the car is wired for positive ground and you have connected the + side of the feed for the electronic ignition module (red wire), from the cars ignition feed line, you may have damaged the ignition module.