Moss Motors, Ltd

While fiddling around in the engine bay of my Mini fixing a problem I had with the carb, I brushed against the coil.  It was cooking hot.  I could not touch it for more than 2 seconds.  I assume this is not normal.  Apart from a faulty coil, can anything else cause this?

The car has a Lucas 25D distributor modified with a Lumenition electronic module and the spec'ed Lumenition coil.

I don't much about Mini's even though I had one for a short time about 40 years ago. Is it possible that you are running 12 volts to a ballasted coil that reqires less voltage? 

Darrel,

With almost any car, if you leave the ignition on long enough with out running the engine, which switches the coil on and off, it'll heat up to piping hot for sure. This is because it stays in the "on" condition constantly. That means there is current running through the primary windings and thence to ground, which is very nearly a short but for the resistance caused by the windings themselves. Heck, this is how a toaster works, and it's whole job is to create heat.

When you must trouble shoot a system which is activated only with the ignition switched on, it's a good idea to take the primary supply lead off the coil. You can shorten the life of the coil, as well as other primary ignition circuit components a bunch otherwise. You can terminate them as well, sometimes!   Enjoy.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

My Bad.  Shoulda stated that I had just driven the car about 10 miles to a friends workshop.  I left the car idling and he hooked up the exhaust gas analyzer.  So we were fiddling around with mixtures etc while the engine was running.  I did not just have the ignition on.  I know this is bad for coils, ignition modules and the fuel pump.  So she had been idling for about 5 minutes when I touched the coil.

Hmmm... Then it sounds like a coil that's being "overdriven".i.e. it's designed to be used in a manner, such as ballasted, other than the way it's being supplied. If it's a six or nine volt coil being fed 12 volts, it's gonna get hot. Check it out.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Thanks.  After some investigation I discovered that the coil needs to be ballasted.  However, with a ballast in place, the spark is too weak and when the engine is cold will not start.  So between a rock and a hard place with this coil.  I have changed the coil to a non-ballasted points coil.  So will see how that does.  Will let you know what the outcome is.

Darrel,

Ballasted coils are meant to get straight 12 volts when cranking . This voltage comes from the starter solenoid and bypasses the ballast. Once the engine is running, and the starter is released, voltage again runs through the ballast. The idea is to overcome the voltage drop caused by the load placed on the system by the big bad starter. Maybe you just have a wiring problem.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Thanks motorbill.  I checked, rechecked and double checked the wiring.  I had done it in accordance to the diagram supplied with the Lumenition.  Anyway, I took the car to an ignition tester.  Unfortunately they were unable to help as the coil is terminal - too many overheating cycles I fear doomed it   So I am currently running on the old points coil I took out when I changed to electronic ignition.  All seems fine and the coil is warm to the touch - not cooking hot.

coils well that ends well. (ouch!)

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Thanks for your help.  Just a quick question on your previous post where you mention that a ballasted coil gets 12v on cranking, then 9v when running.  I assume then your ignition system would be set up to handle this?  The coil was previously, when using points, unballasted.  So I guess the ignition system would not "know" that there is a ballast now?  Some sort of relay required to cut out the ballast when starting?  And then to reinstate the ballast when running.

the ballast is the wire itself Darrel, the wire feed to the coil is resistive! the best solution I find in this scenario is to run a 12v coil (sports coil TT2981) and a new feed wire from the fuse box making sure the feed is live only when the key is turned to the on position and go off when the key is in the off position. A word of warning for future ref is as bill said don't leave the ignition on for any length of time without starting the car! It will overheat the coil and kill the electronic ignition! if you need to check anything on the car with the ignition on pull the coil feed off and the red wire on the electronic ignition module...both usually lucar connectors so easy to remove and replace once your done!   

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Oz Cooper
Classic Mini Product Manager UK


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