Intermittent HT Coil?

[Gary Mac]

Over the last week, I've had a problem with my 1963 2-door saloon stalling once it's warmed up. It starts from cold no problem, but after about ten minutes (choke now in!)it just dies when under no extra load. At first I was able to start it again straight away but today I had to be towed home! The fuel pump is working and the engine starter turns over fine but it wont fire. After leaving it a few hours It started fine but on ocasion stalled with the original symtoms.I spent all afternoon checking Points, timimg and cleaned out the float chamber etc. It starts okay at the moment but i'm a bit wary of it's reliability, and wether to risk it on a journey. Is there such a thing as an intermiitent HT coil fault and how could I test for it?

[Chris Morley]

A faulty coil is certainly possible. There's been several similar postings on the various boards in recent years and from memory it's usually the coil or the petrol pump at fault.







[ This Message was edited by: Chris Morley on 23-04-2002 23:35 ]

[ianselva]

Try taking the top off the float chamber ( switch the engine off first)as soon as it stops, to check that it has sufficient fuel in.This would eliminate the possibility of a fuel feed problem, as although the pump is ticking the fuel line may stil be blocked either by something floating round in the tank or betwen the pump and the carb.

[newagetraveller]

There certainly is such a thing as a coil which becomes faulty when it gets hot. The only way to test it is to replace it with another one and see if your car still shows the same problem.
This may sound extreme but I have two (old) coils fixed on brackets to my dynamo. If one packs up I just change the leads over.
Starting well but stopping after a few minutes can also be caused by a petrol filler cap creating an air lock. This can be tested for by removing the filler cap. However as you say that your petrol pump is still working this is unlikely to be the case.

[stephen]

Are you sure its not the fuel pump?

I had exactly the same problem and tried replacing the coil. But it turned out to be the fuel pump. The more I read about MM's the more this seems to be a recurring drama.

It's easy (if somewhat dangerous) to check. When the problem occurs, turn off the ignition, disconnect the fuel hose from the carb and put the end into a fuel container. When you turn on the ignition again, the pump will tick wildly and fill up the container with fuel. If it doesn't then the fuel pump is sticking. Basically this needs replacing.

Just make sure that you don't spill any fuel onto the engine, or the Minor will rapidly resemble a BBQ

Stephen

[Gary Mac]

Thanks very much Chris, Ian, Newagetraveller and Stephen for your prompt replys. I fitted a new Air Filter, Distributor Cap and fuel pipe between the Pump and Carb. Then also replaced the HT coil with an old one (of unknown reliability!)I was given in a 'Bits' box when I bought the car. Off I went on a test drive and all was fine until at seven miles (about fifeteen minutes) it started miss firing, then stopped with the original fault. As before the engine turned over but would not fire. I removed the fuel filler cap (possible vacuum), fault still apparent. I carefully checked for fuel in the carb float chamber, fault present, tried again, fault still apparent. Removed No 2 spark plug and held it against the block whilst turning the engine over, no spark! Fortunately I was carrying the oringinal HT coil so I swopped over the connections and it started fine. I now have two HT coils mounted on my Dynamo (Newagetraveller style!) and suspect they both fail once hot. So as a tempory measure I will swop between them to get me home, and buy a new one as soon as possible. Just out of interest the Coils are LUCAS HP 12's but in the aforementioned 'bits' box there is another physically different LUCAS HT coil, possibly mini. It's shorter but larger diameter and is marked 'LA12 045200A 9 66'. Does anybody know if it would be a suitable replacement?

[newagetraveller]

The correct replacement is (I think) a Lucas DLB 101. A quick search on the www suggests that the LA12 is used in a Ford Cortina. Do they use different spark plugs and a ballast resistor? The only time I have ever had to make use of my breakdown recovery service was when I bought a new Lucas coil (DLB 101) and assumed that I needn't carry a spare. It went open circuit a month later while I was going round the M25.
Good Luck!

[tuning72]

Hi
This is a common problem and here are just a few I have found; 1st. If the Polarity has been changed on battery(Pos. to Neg.) then the coil connection should also be changed ie; CB.points are on the Earth side. Better still change to a modern coil, suitable for a 12v Neg earth system. 2nd The coil is mounted on dynamo and can fit in any position in clamp. If the terminal is topmost then it can o/heat(out of the oil coolant)Don`t burn your hand finding out? The Vibration does`nt help either. Sometime a new coil has been fitted which is either 9v. or 6v. For use with a "Ballast"resistor, Burns out eventually.
I always fit a new coil on inner wing(shortest distance of HT.lead to Distributer)
Upright.
It often shows up on CB points. A high resistance results in "Burning" and need to change often.
Be carefull with the "Right" part No.Coil They are for an orignal system!
To finish? Original flow is Neg. to Pos. Make sure you have all compatable parts when changing......Ivor......

[Alasdair]

An other altenative is to repace your spark plugs as a faulty spark plug(s) puts a lot of strain on the coil there-for causing misfires and then a compleat ignition failure. hope this is of some help
Alasdair

[rob_dewing]

These problems sound very familiar to me. My 1098 pickup has been eating coils. I've fitted about 5 over 3 years/30 000 miles and I'm getting fed up with it. And likewise I found that the only time I had to call the RAC was when I trusted a brand new Lucas DLB101 and it failed after 3 weeks leaving me at the side of the M4. I'm doing about 1500 miles a month at the moment and I can do without this sort of crap.

Some of the failures have been because the aluminium casing has fatigued through and let the cooling oil out of the coil but some have had no apparent external cause. But I have noticed coils on top of the dynamo run very hot. So I have moved mine to the bulkhead, attached to the 2 bolts that secure the throttle pedal shield inside the driver's compartment. There was no room on the inner wing due to fresh air vent pipe and washer bottle though I considered moving the latter. But I noticed things get quite wet down there and as I've been let down on a few wet mornings I decided the higher the better.

But why so many burnt out coils? I do have Lumenition magnetic ignition fitted and I wonder if that works the coil harder? I don't like setting points so I don't want to give up on the Lumenition and it cost £70.

If anyone has any comments I would be very interested. Meantime I'll see how the coil holds up in it's cooler location.

[tuning72]

Hi
Coils were never a problem on the original Minors, apart that is from general basic faults.
It is only when modifying the ignition system that faults occur. ie;
Changing polarity, great, provided you change every other affected item.
The coil then becomes incorrect and the polarity wrong. ( The Secondary winding become the Primary etc;) The car will still run,but eventually the windings and connections within the coil will be intermittant when Hot.
The same when fitting a Neg earth Alternator. It was practice in the beginning to fit Positve earth types.
Then FM. Radio came along so again did Neg. earth.
The original coil part Nos. were now incorrect anyway. It was practice to fit "Sports" coils. Now we have Electronic ignition. Normally they supply there own coil, if not, then you should contact the Manufacturer for a recommended type.
I will say it was easy money to cure a lot of missfires etc; 2 minutes to change round the coil polarity!

Why has`nt anyone collated answers to problems? Seem to be repeating them all the time.
>>>>>>>>>Ivor>>>>>>>

[Cam]

It seems that there is a lot of confusion about coils.

So, here is a diagram showing the internal workings.



As you can see, the earth terminals of the primary and secondary windings are joined together and contact earth as soon as the contact breaker closes, so if you reverse the polarity of the battery you HAVE to reverse the polarity of the coil, otherwise you will have a permanent (ignition switched) 12v contacting earth directly through the contact breaker (bypassing the coil) which will blow the main fuse.

If you have reversed battery and coil polarity, then there should be absoultely no problem.

Also, from the diagram you can see that it is impossible for the primary and secondary windings to swap places unless you supply 12V down the HT output of the coil!!!

the only reason that windings and connections within the coil may become intermittant due to overheating is when the wrong type of coil is used, i.e. a ballast type coil (6 or 9v) in a non ballast system (12v) as it will be handling much more current through the primary winding than it was designed for.

I have also had experience of the opposite (ahem..), using a non ballast coil in a ballast system (lateish mini), which meant that the spark produced was really weak, as the coil which was designed for 12 volt operation was only seeing 9 (we all make mistakes!!).

I guess that these problems keep reoccuring because new people who have not had experience with these systems are trying things out, and there is nothing wrong with modifying systems as long as you have an idea of what you are doing!!

Cam.

[Willie]

One very simple fault which lead me up the garden for some
time(engine just cutting out when it felt like it) was due to the
coil......traced to the fact that one of the two connections on the
coil, which was rivetted in postion, had worked very slightly
loose and went intermittent. A gentle tapping on the rivet cured
it. The simple ones are usually the hardest to find!!
Willie

[Cam]

Willie,

The simple ones are usually the hardest to find!!

And often the most satisfying to fix!!

Cam.

[Sparky]

I had exactly the same problem as Willie...i.e. the two connections on the coil had worked slightly loose. I would be driving along merrily then after about 5 miles would grind to a halt with classic symptoms of overheating and would not restart for around twenty to thirty minutes after.
Needless to say I went round the houses before eventually coming across this problem....not excessively loose, but just enough ! Coil got really hot, I tightened up the spade connector fittings and bingo problem solved..... Always the simple things eh?

[Willie]

Very true...it's a pretty good motto
"THINK SIMPLE."
Willie

[rob_dewing]

The picture of the innards of the coil helps explain things thanks - get it wrong and you are putting the HT through the primary as well as through the secondary. No wonder the insulation breaks down, though there won't bw much potential difference between earth and the far side of a few ohms of primary. But the new coils are simply marked '+' and '-' not 'IGN' and 'CB' like they used to be. So if I am buying a coil designed for positive earth and putting it onto a vehicle converted to negative earth, do I really need to connect the coil back to front i.e. + terminal to earth even though I know earth is now -ve? This is doing my head in but it might be worth trying. How else can you determine which terminal has the connection to both windings? Resistance won't be detectible with secondary at several kohms and primary at about 3ohms. Maybe I should get onto Lumenition and ask them.

[Cam]

Rob,

If you are buying a coil designed for positive earth systems, and your car has been converted to negative earth, then reverse the connections.

On a negative earth car, IGN = +, and CB = -
other way around for pos earth.

You need to have the two earth terminals of the coils (primary and secondary) joined together inside the 'coil' otherwise the circuit will not be made, this corresponds to the '-' terminal for a neg earth car, and '+ or CB' for a pos earth car.

In other words, if you buy a Minor coil, reverse the connections, if you buy a neg earth coil keep the connections as they are.

[rob_dewing]

Thanks for the advice Cam re back to front connection of the coil. The picture got me thinking and I found one of my failed coils which I hadn't got round to binning. I hacksawed round the case to open it up and lo! there were the two wires to the + terminal and one to the - terminal. So + and - are only correct if you use the coil designated for positive earth on a positive earth vehicle. If you change to negative earth......leave it alone even though electrical practice says the markings are wrong!

It would be far better if they'd just left the coils marked CB and SW like they used to be. But this still doesn't excuse the two or three Lucas coils I've lost due to the oil leaking out.

[Cam]

Yes Rob, it would be better if they left the markings as IGN(SW) and CB.

But as usual we are left behind by spares manufacturers!!

I suppose ours is a small market compared to the other modern stuff.

Incidently, it will all change again in the next few years anyway as cars are produced using the new 42 volt system.

I went to an IEE lecture the other week on the reasoning behind the new system, and the chap giving the lecture did a brief history of automotive electrics and right at the start (in the dark and dismal past) was a Moggy starter motor!!! A fine example of old and decrepid technology.

Made me chuckle to myself anyway!!