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MG Midget and Sprite Technical - Ignition mystery

Here's the scenario,
Driving along perfectly, wind in the hair, smile on the face, when suddenly the engine cuts out and the car coasts to a halt. After a few turns on the starter it fires-up and runs perfectly again. This is an intermittent fault that dogged the car last season and is doing it again. Sometimes I can complete a journey with no trouble at all, at other times it can happen three or four times during the trip.

I have replaced all the HT components and apart from the above, the engine runs well, so I am thinking that it must have something to do with the Low Tension side of the electrics or ignition switch.

I did notice that when I changed the points (my first time with a Triumph engine)that the LT wires are a very loose fit where they slide into the hooked end of the contact breaker spring (two wires connected to a common plate similar to a spade connector)

Any suggestions would be appreciated!

Dave
Penwithian

Dave. Does your car have an ignition relay? If so, I have seen them go bad and cause the problem you describe.

Les
Les Bengtson

Rotor arm?
Dave O'Neill 2

Had the same problem, or symptom. It seems that a bullet connector under the dash had a smidgen of rust, and upon running the headlights, wipers, and rasio simultaneously the heat running through that connector caused a temporary short. After a few seconds, the car fired up and I proceeded nervously to work. It happened again the other morning and I cut the radio off and the engine fired up pretty quickly while I was still rolling. Man, I hate crawling around under that dash!
If it was just the engine that died, it may be another problem, but if EVERYTHING died, I'd try re-creating the symptom to isolate it and be sure. Try driving up and down your street with EVERYTHING on and see how it goes.
J London

Penwithian,
Is this on the 76 or the 79?
What does the tach do? If it is a low-tension fault, the tach will drop like a rock immediately. If it is high tension, the tach will go on its merry way.

It really sounds low tension to me. In fact, it sounds a lot like a split bullet sleeve. It also sounds a lot like an intermittent electronic fault. You mentioned points, so I don't suppose that you have retained any of the imaginative Lucas electronic ignition stuff?

If it were my car, I would rig up a test light in the cockpit with one lead screwed to a good ground and the other having an alligator clip or similar in the engine compartment. I would start by clipping the lead to the + side of the coil and seeing whether the coil is losing power when these things happen. If so, try it at the white wire where it comes off the ignition switch. If you are losing power there, walk back along the brown wire that feeds the ignition switch, bearing in mind that it is allways hot, so you will want to disconnect from it when leaving the car.
Gie us some feedback, eh?
David "Maybe it is the condensor" Lieb
David Lieb

I agree withh david,

This is most likly going to be a stupid little thing like a bullet connector, a loose wire connection, or minor corriosion somewhere in the system ....maybe even a 90% broken spade connector....when you find it, you will know it almost right away....but it will be a bear to find it, most likely it will take all day just running down your ingnition wires. looking for any kind of out of place fault..buts its most likely between the dist/coil ...and the tach/ignition switch....Id also look aat the brown wires for any breaks or rub areas....


good luck
prop
Prop

Dave, have you looked at the back of the ignition, I have this problem with mine and just jiggle it at the back, where the plate at the back is loose. This was an ongoing problem with mine for months and I've recently discovered the lose plate. Will keep jiggling until I get round to a permanent solution.
Paul
Paulgertie

Like someone above says:

- Did you replace the rotor arm? (Maybe these are fine on the 1500s?)

- Have you checked all connections on LT? Esp on the ignition barrel (white, white black wires)

- Does the r/c show 0 rpm when the ign cuts and the engine is still being driven.

Also consider the fuel pump. These can stop working, and yet be revived with ign being switched off and on. In fact, switching the ign off and on can cause a faulty pump to send a pulse of fuel down the line, ready for the car to start and run for a few secs. Next time the ign cuts out, carefully (partially)remove the fuel pipe on the carb and check if there's any pressure.

A
Anthony

You say that you've changed all of the HT components . . . . did you replace the coil? My experience is that HT coils can go intermittent once they become warm.
Andy Hock

>>> Also consider the fuel pump. These can stop working, and yet be revived with ign being switched off and on. In fact, switching the ign off and on can cause a faulty pump to send a pulse of fuel down the line, ready for the car to start and run for a few secs. Next time the ign cuts out, carefully (partially)remove the fuel pipe on the carb and check if there's any pressure. <<<

1500s have mechanical fuel pumps, so unless Dave's running an electric replacement, you can probably rule out the pump.

I suspect David L. was only half-kidding above when he suggested the condenser. If you haven't tried a different one yet, it couldn't hurt. I had a dickens of a time with mine a few years ago, with repeated roadside head-scratchings until I figured out what the problem actually was.

-:G:-
Gryf Ketcherside

Sorry for the late response folks, been too preocupied with the intermittent fault.
I took the cowards way out and got my son to check it out, his limbs are a bit more flexible than mine for getting under the dash etc. He checked all the connections and retimed the ignition with a strobe light and all seems OK for now.
I was just thinking over the suggestions you all gave for the possible causes. It's the 1979 car and yes, when the fault occurs the rev counter drops to zero.
If and when it conks out again, I must remember to look at the ignition warning light to see if if it has gone out. if so, if the ignition key was still in the on position wouldn't that indicate a fault with the ignition switch?

Dave
Penwithian

This thread was discussed between 07/05/2008 and 13/05/2008

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