How to tell what type an ignition coil is?

[yorkshire_spam]

Related to my recent issues... how can I tell if a coil is 12v, 6v, or ballasted type?

I have spares I want to test, but the Dolomite ignition is ballasted type - so I want to make sure I don't randomly fit the wrong type of coil.

 

[Dannyb]

With a volt meter set on ohms.  Ballast should read approx 1.5  and non ballast 3 ohms. 

Danny

[yorkshire_spam]

Thanks Danny

 

[standardthread]

It may not be so obvious.

The previous owner of my Dolomite, last but one ever built, had significant issues with the ignition and coil before and after fitting electronic ignition.

He and an auto electrician thought that the resistor could be in the loom somewhere. I will try and contact him to see exactly what he did.

[yorkshire_spam]

I definitely have a resistor and it's all connected up as expected. Voltages are what you'd expect when running vs cranking. It's telling the difference between my other spare coils I'm asking about. 

[standardthread]

The issues he had were repeated hot coils, miss fires bad starting when hot etc..

He and everyone including the auto electrician thought his (my) car, 'Y' reg., had a ballasted resistance coil with the resistor wire buried in the loom (no external resistor as per my previous 'V' reg Dolomite).

To overcome repeated hot coils he put a separate resistor with direct feed in the engine compartment.

He was also told that if the voltage to the coil is battery voltage then it isn't resistor fitted, if it's 9volts or thereabouts  there is a resistor somewhere in the system.

He knows an ex BL apprentice and there were issues known about but not published because parts were swoped between models because of availability of parts .

On the Dolomite forum he was known as Robsun

 

[RobPearce]

15 hours ago, standardthread said:

He was also told that if the voltage to the coil is battery voltage then it isn't resistor fitted, if it's 9volts or thereabouts  there is a resistor somewhere in the system.

That's an oversimplification and can give misleading results if applied naively. The voltage at the coil +ve will be battery voltage regardless of coil type when the points are open. On a ballasted coil it drops to 6V with points closed, but not instantly. Although it's faster than you could measure with a meter, it will affect the reading you get with the engine running, which has so much noise on it that a multimeter probably isn't useful.

[standardthread]

Hi Rob,

Only quoting what he found and the difficulties he and the auto electrician have over the five hours it took them to find and sort the problem and the simplified explanation he gave me over the phone.

[Dannyb]

I had a problem with the ballast wire that had gone high resistant.  So i just took a new feed fron the ignition live and fitted a 12v coil.

Remember to fit the coil the correct way round +ve - ve.  It will run the wrong polarity but will give misfire later when get hot. 

Danny

[standardthread]

3 hours ago, Dannyb said:

I had a problem with the ballast wire that had gone high resistant.  So i just took a new feed fron the ignition live and fitted a 12v coil.

 

That's the problem Robson had, only the book said it was a resisted circuit (in the loom) but he found no resistance in the cable after buying an expensive ballasted electronic ignition kit.

The BL apprentice he knows worked on other BL vehicles such as LDV's in the late 70's and some should have had resistance cables but they hadn't and were causing issues for dealers but BL kept quite.

[RobPearce]

2 hours ago, standardthread said:

That's the problem Robson had

Sorry, no. re-read Danny's words that you quoted and you'll find it's actually the exact opposite of the problem you say Robson had.

[standardthread]

15 hours ago, RobPearce said:

Sorry, no. re-read Danny's words that you quoted and you'll find it's actually the exact opposite of the problem you say Robson had.

The point I was trying to make was that Robsun thought it should be a resistance loom according to the book and build date, and, he though he may have had the same problem as Danny had, but BL had used non-standard, but identical looking parts (in a number of different models), cable colour etc.. That's why it took an auto-electrcian five hours to find and sort the problem.

Had Robsun not gone by the book and purchased a 12 volt electronic ignition system, gone against the book, there would never have been the problem.

It was only when he talked to the ex-BL apprentice that he found it a 'common' problem in the trade.

But it raises the issue that there may be owners out there who think the same, resistance loom, but in fact it isn't.

Edited August 28, 2022 by standardthread

[yorkshire_spam]

Pretty sure I have a ballast resistor and no resistance wire in the loom.

I see full voltage at the feed to the resistor and as far as I'm aware the loom hasn't been replaced and they weren't fitting looms with resistance wires to Dolomites when the car was built in Jan 1973.

 

[standardthread]

You have the same set-up as I have but my resistor is mounted on the suspension tower with a separate direct feed from the fuse box. But according to spec. (drop down boxes used by suppliers etc.) the car should have had a ballast resistor. Because Robsun couldn't see one he presumed it was in the loom (as per Danny's issue?) and according to his research.

As I said earlier my car is last but one 1300 built in 1980, registered in 1982, hence 'Y' reg! The only one known.