Coil? Or something else...

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Drivemaine
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Coil? Or something else...

Post by Drivemaine »

I recently went through a no spark issue in which turned out to be a bad coil. Long story short prior to diagnosing the faulty coil my ‘57 Minor came to me with a Petronix ignition which had a bad pickup. I replaced the unit with points and condenser, and then bought the coil as I had the no spark. Car ran great for a few weeks, until last week it started to stutter a bit while cruising (not accelerating, as it would start to clear up.) today however, the car suddenly coughed, backfired (sounded like intake) lost power (I would say spark) and then stalled. I got it going very briefly then it stalled again. Upon getting the car towed home I made sure fuel was flowing properly and that the bowl was clean. All looks good to go in that department. I then pulled the king lead from the distributor and cranked the car and found no spark. Again this is a new coil. I have several spares kicking around including two new ones. I hooked them up just to see if there was spark and sure enough there was. However when I connected it to the distributor the car would start very rough idle for a moment then stall. When I pulled the king lead again to check for spark there is none. I swapped the coil with four other coils and found this problem with each of them. Surely it isn’t all the coils that are bad. Could it be an ignition switch issue? I checked wiring and found no obvious chaffing or damage. I’ve got power where it needs to be and good resistance in the coils...any help would be great! The car had been converted to a 1275 unit. I have replaced points, condenser, plugs, wires, and coil prior to today’s events
Drivemaine
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Re: Coil? Or something else...

Post by Drivemaine »

I also wanted to clarify that the coils would not show spark after the king lead was again removed from the distributor, though they showed spark prior to hooking them to the distributor. I was thinking perhaps the lead itself could be bad and work when it is in a certain position...but the odds I got it in the right position each time with each different coil seems remote. The car is also a negative ground vehicle
StillGotMy1stCar
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Re: Coil? Or something else...

Post by StillGotMy1stCar »

I apologise in advance for suggesting this, but have you checked the points gap. The nylon heel on the points can wear quickly if the replacement distributor hasn’t been used for a while, re-adjust and a dab of grease should sort it.
Wishful thinking for an easy fix perhaps!
Regards John.
Drivemaine
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Re: Coil? Or something else...

Post by Drivemaine »

No need to apologize at all! I appreciate any advice. Considering the ignition system is about as basic as it can get, for some reason it has me flummoxed. I rechecked the point gap just to be sure, and it is .015 which is what it calls for. I have 12v on both sides of the coil and a resistance reading of 4.23 between the terminals. I did continuity checks on the wire going from ignition switch to the coil then also check the low tension lead continuity as well. All checked well. The ground lead inside the distributor also has continuity as well. The ground strap is sound and clean and I even had added a secondary from block to frame a few weeks back (I was a Alfa Romeo mechanic for quite a while and then went on to aircraft engines and learned you can never have too many grounds.) l just for the life of me seem to figure this out at the moment. Like I mentioned earlier I can’t believe all 4 coils are bad, especially since they had spark when disconnected from the dizzy, and then after trying to start the car to no avail, when the king lead is pulled and rechecked for spark there is none...I suppose something could be shorting them out when attached to the distributor....
Myrtles Man
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Re: Coil? Or something else...

Post by Myrtles Man »

Your replacement condenser isn't one of the many duff ones that are available now by any chance is it?
pgp001
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Re: Coil? Or something else...

Post by pgp001 »

You could try eliminating the distributor from your tests, with the ignition switched on just dab a wire from earth onto the points connection on the coil and see if you get any spark from the king lead, the spark will occur as the wire is removed from the terminal which is simulating the points being opened. It is not going to be as good a spark as normal because no condenser is present, but it should tell you if the coil has any life in it still.

If just having the coil in the circuit gives you a spark then you know the trouble lies in the distributor somewhere, ie points, condenser etc.

Phil
myoldjalopy
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Re: Coil? Or something else...

Post by myoldjalopy »

In addition to the above, have a good look at the condition of the king lead where it goes into the coil, and whether it goes in tightly - might be a dodgy conection, made OK when you first push it in, but then loosening as you try to fire the engine.
oliver90owner
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Re: Coil? Or something else...

Post by oliver90owner »

Current through the coil is necessary. Voltage either side of the coil will be 12 volts while the points are open but this does not mean there is sufficient current when the points are closed. You should be finding about 3 amps through the coil to earth. If the current is low, suspect a high resistance in the supply (when current is drawn and a poor joint/connection heats up, reducing the current). If that checks out, measure the current with the points closed. It should not be substantially different,

With the points closed - If there is resistance after the coil there would be more than zero volts on the points side of the coil; if before the coil, there would be less than supply voltage at the coil on the supply side. Should be easy to check, one way or the other.
Dogsdad
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Re: Coil? Or something else...

Post by Dogsdad »

When I had a similar problem years ago the cause turned out to be a faulty rotor arm shorting from the brass
strip on top through to the drive shaft.
Have you changed the rotor arm?

R.M.
oliver90owner
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Re: Coil? Or something else...

Post by oliver90owner »

Dogsdad wrote: Thu Sep 19, 2019 10:52 pm When I had a similar problem years ago the cause turned out to be a faulty rotor arm shorting from the brass
strip on top through to the drive shaft.
Have you changed the rotor arm?

R.M.
The rotor will have no effect on spark from the king lead to earth - unless there is something extraordinarily wrong inside the distributor, which should be very obvious on inspection! The rotor is there to distribute the spark, so only carries high tension voltage. Opening the points with a suitable screwdriver, or similar, is a simple diagnostic ploy to avoid unwanted aberrations while testing the circuit.
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