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MG MGB Technical - Engine just stopped now no spark?

Hi all,

got a problem with my MGB
engine was running OK and then dropped a cylinder or 2 and then stopped.
Now will not start
no spark at plugs when cranking
no spark direct from coil when cranking - put a HT lead in top of coil and rested plug on engine)
Doing above method if i open the points with a screw drive the plug sparks.
I have tried different dizzy cap and leads

running out of ideas appreciate any suggestions

Steve D

Steve - Sounds like the points closed due to wear on the rubbing block. If the block has not worn completely down, you should be able to re-gap the points and get your spark back. Cheers - Dave
David DuBois

Steve. You state that you have no spark from the coil lead when turning the engine over. Later, you note that, "Doing above method if i open the points with a screw drive the plug sparks.".

This indicates there is a problem in the low tension circuit and the problem relates to the points not opening properly. When you open the points manually it triggers the coil and the coil lead fires. Check the points gap and the ground wire from the points plate to the side of the distributor.

Replacing the distributor cap, leads, rotor should not be done until the low tension circuit problem is corrected. Then, replace parts, one at a time, as necessary.

There is an article on ignition system troubleshooting on my website, on the MG section.

Les Bengtson

I had similar symptons - diagnosis indicated that either the rotor or cap was shorting out. Replacement of both solved the problem.

BJ Quartermaine

Thanks for the suggestion. I will try checking the points. They are definitely opening though as i can see an air gap

Steve D

Just ordered a new dizzy cap, rotor, condenser and points.
I'll give that a try.
Interesting website Les - now added to favourites
Steve D

this happened to me a few weeks ago, done what you have and new points plugs coil and cap still nothing.
called out a mobile car sparky in the end by the time i,d made him a cupa he had the car running!
problem a wire had dropped off the back of the rev counter!
worth checking
s truman

The statements don't add up here. If there is no spark, but flicking the points open by hand produces a spark, then what Les says about the points gap having closed up is correct. But then you say you have a visible gap. The only way that can happen is if when the cam opens the points the spring of the points is shorting out on the cam, or other metal parts in the distributor, but it isn't when you open them by hand. However maybe they aren't *closing* properly, due to mechanical failure or burning of the contact surfaces, and it is when you arwe shorting them out and removing the short that you are getting the spark.

If it's the cap or rotor then with a timing light on the coil lead it will flash but won't when connected to one or more plug leads.

If it doesn't flash on any lead you connect a voltmeter or test lamp between each coil terminal in turn and a good earth and while cranking watch for the meter switching between 12v and 0v (lamp switching on and off) when it is on the white/black points wire (coil -ve) and being on all the time when it is on the white wire (coil +ve).
Paul Hunt

hi again all,
finally got to the bottom of it after new leads, plugs, dizzy cap, rotor arm, points.
Is was the coil!!
strange how it sparked manually though but would not run the engine

thanks for the ideas
Steve D

This thread was discussed between 25/07/2009 and 30/07/2009

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