Wierd ignition problem

[Rich_s]

Over the last few days my car has started coughing while driving, tickover is fine, under 1500rpm is fine, while driving down the motorway it will be fine for a few miles then start coughing, like someone has turned the ignition spark off for half a second, it will do it a few times then return to normal and all works perfectly for another few miles, the plugs are all fine, timing is fine, contact removed, cleaned and reset, new dizzy cap, rotor arm ok, new ht leads, only thing i can think is that the coil is failing?

any one any ideas?

thanks in advance
rich

[sparky_spit]

I think you could be right. My 1st choice would be rotor arm breaking down after 15 mins or so, 2nd choice would be the coil. Only way to tell for sure is to replace each with a 100% known good one. Do it one at a time and test for a few days so that you know which was the culprit.

[drofgum]

Rich,
I have had a similar problem with my MK2 Spitfire; it turned out to be a worn out ignition switch. So check your LT connections.
                                                       Cheers,
                                                       Paul

[Steve Cureton]

you say the plugs are fine but I would try changing them as I have known them to break down in this way.

[Rich_s]

Thanks for the replies guys, that gives me something to work with, i think i have a spare rotor, if not ill get one, i did notice it is one with a rivet in the middle which i think i read somewhere on here is a bad thing, doubt i have a spare coil unless one from an MGB fits, could try it i suppose.

The plugs looked new when i got the car about 4000 miles ago so would think they are ok but if the roor and coil don't fix it ill fit some new ones.

thanks again for the help
Rich

[GT6Craig]

Try a bit of contact adhesive ont rotor arm as poor repro ones can wobble and bounce off during use!

[Pete Lewis]

riveted rotors are notorious,  get a coloured one from rarebits or other good suppliers

easy rotor test is take dizzy cap hold the coil HT lead 10mm above the rotor , get  the engine cranked over
if a spark jumps to the rotor its stuffed and earthing from the rivet down via the spindle.

also check the coil 12v  is polarity correct

Pete

[Rich_s]

Thanks for the responses guys, been checking and found my dads mgb has the same coil and distributor, so going to swap the rotors and coil, one at a time and see how it goes, if the rotor fixes it ill get a blue one from rarebits, thought i had a spare but as usual, think i have thrown it out, typical.

rich

[Velocita Rosso]

When youve checked that please let us know if you have cured or not. I had a similar experience some years ago with the same symptoms. Dont want to mislead at this point if you are going to experiment with the leads and cap

[CharlieB]

Another possibility is the ballast resistor, which is a pink/white wire built into the loom on the 1500. Mine would cut out completely at random moments but I could always start the engine again (even before the car had stopped) & drive a few more miles before it happened again. Took me ages to find the problem  :(

[Rich_s]

Just tried a known working rotor arm and no difference at all, still the same, might get chance to try a new coil 2moro, will let you know what i find.

rich

[dazzer]

Hi Rich

Speaking as an ex BL mechanic, before you do anything else, please just replace the points and condenser together.

The intermittent miss/cough sounds very much like the points sticking momentarily because the condenser is not doing its job properly

The number one culprit is nearly always points and condenser. My advice would be to always replace the points and condenser together rather than clean them.

Hope this helps

Cheers

Darren

[Rich_s]

Hi Dazzer,
Funily enough i had just thought about this, even though the points are only 1000miles old, i am going to put back on the old ht leads and spare dizzy cap and old points and condensor, all know to be working fine, they just got changed as were old and grubby, praying this cures the problem, then can narrow down to exact problem, if this does not work i will be testing a working coil on it 2moro, will report back what i find.

thanks
rich

[Rich_s]

FINALLY.................

I think i have cured it, tried different ht leads, no change, diff dizzy cap, no change, put on another condensor, no change, noticed the condesor to coil wire termial knackered, thought that would be it, tried it and no change, put it all back an thought i would try the old contact breaker, even though the new one was fitted at the end of november and only done 1500 miles, hey presto car no runs sweet again.

Not known them fail this quick before but guess just one of those things, will get a new set of points 2moro and keep the old  working one as a spare.

Thanks for all your help guys, feel abit daft now as it iwas something so simple, at least its working ok again, for now....

thanks
rich

[don cook1]

And now you know a lot more about your car!

[Steve Cureton]

A knackered condenser (sp?) will cause the points to fail, and as they're only cheap it's worth replacing. Failure will be evident by pitted/burned contacts.