Exploding HT Coil

[Nickl911]

Hi. There I was trying to trace voltage problems with the flapper and throttle pot with the ignition on so as I could measure voltages when the HT Coil exploded in oily white smoke. After panicking and headless chicken stuff, I have a question....

The dizzy is a points only dizzy (because previous owners have swapped loads of bits and I'm trying to restore it to bog standard 1985 350i).

Taking the dizzy cap off shows the points are closed.

Therefore for half an hour or so, 12 volts are running through the coil to earth via the points.

Is there a device missing that will stop the coil overheating? Just leaving the ignition on with the engine stopped will fry it surely?

The coil has a wire to the positive terminal and a capacitor to earth, while the negative side goes to the dizzy and to the EFI ECU to provide the pulse to fire the injectors.

It definitely is not electronic ignition so I can't find a suitable wiring diagram for it yet.

Any ideas please

[adam quantrill]

Yes - put in a standard electronic dizzy or you will suffer the same fate some time.

The standard one won't energise the coil except when there are pulses in the pickup, and when the engine is stopped there are no pulses.

[Nickl911]

Thanks for that, I'll try the electronic route.

[Penelope Stopit]

You don't need to change anything away from standard, In years gone by it was standard practice to disconnect the ignition coil when leaving the ignition on for anything other than starting the car

[Nickl911]

Well I just measured the resistance across the terminals and it shows as approx 1.6 ohms, which I now think is a 6 volt coil (??) so no wonder it fried. I presume it previously had a ballast resistor inline to reduce the voltage. But that's only from what I have read recently online.

As mentioned, previous owners have changed so much I'm struggling to get to a baseline.

Still I'll keep trying to work it out.

Thanks for comment.

[John042]

Been there Nick. 2.8i cutting out after a few miles. Ballast resistor system probably bypassed by previous owner, retaining original coil. Solution, rewired fused 12v supply direct to new quality 12v coil.

[Nickl911]

Thanks John, good to hear it has worked before