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MG Midget and Sprite Technical - Intermittent ignition problem......

HI folks,
I've been having an ignition system problem in my '76 midget for the past month or so. All of a sudden, the engine will quit like someone cut the ignition wire. I'll coast over to the shoulder, pop the hood, start checking wires like the coil wires, distributor wires, plug wires.....Then when I get back in the car, it starts.
When I play with the wiring connections with the engine running, I can't get it to quit.
I was starting to think that maybe it was the coil. It seems to happen on hot days and the coil felt quite hot today when this occurred. Is it possible that being off for a minute a coil could come back into spec ?
I can't think of anything else.
Does anyone have any ideas?
Thank you for your help.
Paul
Paul W 1976 1500

I've had issues like this with a dodgy coil and points where the heel wore quickly and closed the points gap to almost nothing and closing on the engine heating up. On both occasions though it required around half an hour for things to cool enough for it to be started again.
David Billington

My guess would be the rotor arm. My Sprite would run for about 20 mins then cut out. It would re-start after a 15 min cooling off period.

Make sure you've got a red rotor arm. Mine came from MGOC but the Distributor Doctor is highly recommended: http://www.distributordoctor.com/

It could be the condenser, the Distributor Doctor's are much better than most of the other current 'over the counter' items.

C

P.S.
Paul, I just noticed your location - there MUST be someone your side of the Atlantic who does the red rotor arms and higher spec. condensers etc.
Colin Mee

Check the low tension wires insulation inside the distributor very carefully. I have had the same thing happen and its hard to find because as soon as you move them it starts and the split in the wire was very small but enough to short it out if it got in the right place. Probably the result of rubbing a bit on the shaft at some time.

Trev
Trevor Mason

Do you have the pertronix ignition chip ...if so, BING0 ! Its called phazing

Prop
Prop and the Blackhole Midget

With Trev on this, but I'd like to add that if you have access to a megger, or a friendly electrician with one, you might test the isolation between the primary and secondary coil windings. It might be breaking down. Also check the coil body is securely earthed ('scuse me - "grounded"). I had this happen many years ago on a Mk3 Cortina and it turned out to be poor coil earthing. I still don't understand why the temperature of the coil affected it, but it only happened when it got warm.
Greybeard

PS:

"there MUST be someone your side of the Atlantic who does the red rotor arms and higher spec. condensers etc."

.........

If not let us know and I can get them in the mail to you if you need 'em.

Cheers.

Rod.
Greybeard

Check all earth/ground connections and LT leads. Ensure there is metal to metal contact, and they are all secure. Failing that it could well be the coil breaking down - change it - cheap enough.
Mark O

When it happens, what is happening for instance with the petrol tank level? Also down?
Bad connection in the ignition switch?
J.W. Vlaanderen

Thank you for all your suggestions guys.

I'll have to get back in there and check things out further.

Paul
Paul W 1976 1500

I had this once on my 1500, drove me mad until I traced to a faulty ignition/starter switch!
SR Smith 1

Well, this morning I pulled the coil out and cleaned up the body to assure a good ground. Cleaned up the spade plugs on the coil (Thought one of them was loose. One of those spade adapters screwed on the coil. You want to find stuff like that, so I'm not sure if it was my imagination.)
Took the car out for a 20 or 25 mile run. All was going great until about a mile from home. I coast into a parking lot, open the hood and just touched the wires on the coil and the high tension lead ends going to the coil and distributor cap. It fires right up. It died again 10 houses from mine. Opened the hood, probably touched the same wires, fired right up. Pull in the drive, it dies again. I'm not even sure I touched anything this time, just opened the hood, looked and went back to the key. Fires right up.
I just ordered a new coil. That thing sure was hot. My fingers aren't usually bothered by temps, but I couldn't have kept them on that coil for long.
I'm starting to suspect the starter switch too SR. Interesting. Next time, if it quits while I'm at a decent speed, I'm going to turn the key off and back on again. (This is starting to make me a little nuts) I won't be driving it until next week now, but I'll be sure and keep you all posted.....
Paul
Paul W 1976 1500

Paul I suspect your coil, for what it's worth. Nothing wrong with it getting warm,but I don't think it should get too hot to touch. To me that suggests the isolation breaking down between the windings of the coil. It seems like there may be a "leak" from one side to the other with a high resistance which generates heat, to the point that the coil no longer generates the voltage needed to supply the spark.
I think (and hope) you've done the right thing buying a new coil. But I'm interested in why you suspect the starter switch.
Good luck anyway.
Greybeard

Hi Greybeard,
Thanks for coming in again.
The only reason that I start thinking about the switch is that it seems like I'm not doing anything to correct the problem and then the engine starts back up. I am turning the key off and on though......
But opening the hood and touching a couple wires can't be helping. Especially when I can't get the engine to quit when I jiggle wires around when it's running.
Yes, I'm hoping the coil will be the answer. The ballast resistor was awfully hot too.
I'll have that coil next week and then we'll see.
Until I know for sure, I'm spending most of my time in the right hand lane (Slow lane) so I can get off the road when it quits. Today was the worst , by far. Quitting 3 or 4 times within a couple of minutes. (That is one more factor pointing to a heat thing).
Paul
Paul W 1976 1500

I fitted a new coil today. The diameter was just a little larger than the original, so I had to do some minor bracket modifications.
Got to go for a 20 mile spin and so-far....so-good. It wasn't all that warm today though. It was on the hot days that I had trouble. Today was 10 to 15 degrees cooler. It's probably taken care of though.
Thank you all for your help and suggestions.
Paul
Paul W 1976 1500

Good stuff, Paul. Hope there's no more trouble.
Greybeard

This thread was discussed between 28/07/2015 and 06/08/2015

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