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MG MGB Technical - No spark

1972 B JUst got her back on the road for the first time this year last weekend. Had driven about 20 miles when the engine died. It turned fine and at first i thought it was a lack of fuel, fuel pump. But after having it towed home the pump was working fine.
1/ No spark at plugs
2/ Spark at points in distributor, even better spark now i have peplaced the condensor/capacitor
3/ No i don/t know to use a volt meter

Could it be the coil ?

Please help
Gerry Lodge

Replace the rotor, preferably with one from Advanced Distributors http://www.advanceddistributors.com/ Cheers - Dave
David DuBois

Could be the coil - could be the rotor arm - could also be shorting out in the distributor.

This happened to me the other week in a new car, and, after we checked everything out, it turned out that, when driven by me (and not the previous owner), the spring was shorting out on the inside of the outer cover of the distributor.

When I mentioned this in a "who had the worst weekend" discussion, I was told that this is quite a common fault in a B ....! So, anyway - it's worth a check, and free :)

(Not long after that, my BGT did exactly the same thing - it wasn't shorting out, it was due to a previous owner having changed the wires between the coil and distributor and there must be a loose connection or something, but I've not had time to check that yet!)

There ya go - couple of cheap ideas for ya from the last couple of weekends in my life!!!!
rachmacb

Remove the centre wire from the distributor and hold it close to an earth whilst flicking the points. You should get a good spark if not it is most likely a coil fault if you do then it is likely a rotor arm or distributor cap fault.
Iain MacKintosh

As Aian says
Remove the dist. cap
Remove the coil lead from the cap but leave the other end in the coil still. Hold the free end of the coil lead 1/4" away from the engine block or a good earth point and crank her over on the starter -- you should get a spark jumping the gap -- if not the coil or lead are faulty
If you do get a spark you can then test the rotor button by holding the end of the lead above the centre of the rotor button instead and cranking her over
If you get a spark jumping to the rotor it means the rotor has a leak to earth and needs replacing
In the odd chance that you have spark to the block but nothing to the rotor the only remaining posibility is the ditributor cap - in this case check to see that the carbon post that rubs on the centre of the rotor is intact, if it is ok you will need to get someone to measure the resistance through between the outside and inside centre posts of the cap. It's very rare but I have seen a cap go open circuit through there
Hope this is of some help - Willy
Just read rachmach's post, have a good look at the cap on the inside and outside near the clips, if it has been sparking there you should see little marks in that area that look like the lead out of a pencil burnt onto/through the cap
William Revit

Sparking at the points is bad. The capacitor should stop this. I doubt the coil is faulty. It must pass current to get the effect at the points. I would clean and gap the points and try a known good capacitor.
Stan Best

Thanks for all your help guys. I bought a replacement coil but no difference, I then noticed the wire,spade connections weren't that good at the coil and the earth wire in the coil. Put new spades on, cleaned everything up and shes on the road again. Life is good.
Gerry Lodge

This thread was discussed between 06/05/2011 and 08/05/2011

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