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MG MGB Technical - Ignition Problem 68BGT

OK, here's one for greater minds than mine to mull over.........About 2 years ago I purchased a lumenition magnetronic ignition. All was fine until recently the engine would cut out after about 20mins driving. If left to cool for an hour, it would start fine and continue in this cycle ad nauseum. Last weekend it refused to start at all. Refering to the BBS Archive I discovered that this was not uncommon with the Magnetronic kit. I therefore replaced it with an Aldon Ignitor alternative (and a new coil for good measure). Still no joy.

Symptoms as follows:

Turn ignition key: No ignition light present(!?), fuel pump chatters away until primed.

Turn fully: Engine turns well with a fat spark being emitted from the coil when tested. NO SPARK at the plugs however.

I'm starting to worder about the ignition switch.......or am I barking up the wrong tree? Any suggestions welcomed.....
Andy Hinson

If you have spark at the coil, but concurrently not at the plugs, my guess would be that your problem is between the coil and the plugs. Wires, cap, rotor.

If you use graphited core wire, that can break down after a few years of use or quickly if routed too near high heat (not necessarily a problem in an MGB). You might have a temp sensitive dizzy cap ~ if so, that should be getting more difficult to live with as time goes by. And if it is your rotor, and you have one with a radio suppressor in it, the suppressor (usually a carbon resistor of some sort) could have broken down as well. I never use the suppression rotors, only the all metal conductor type if possible.
Bob Muenchausen

Fixed! New dist cap and rotor seem to have done the trick. A case of 'Keep it simple, stupid' I think.....
Andy Hinson

The fact that you get the pump to work and a fat spark at the coil would indicate to me that the ignition side of your switch is ok but your Ign light may have burned out or you have a loose connection between the switch and the bulb. When the engine is not running, current to the bulb comes from the battery/ignition side of the bulb circuit.
Bob Muenchausen

Andy. As Bob noted, the ignition system problem is not part of your charging system warning light if you are getting spark at the coil lead. It might be an ignition switch problem if you were not getting any spark. The fact you are getting spark indicates that the ignition relay is being powered by the white wire circuit. Your ignition warning light is also partly on this circuit with the brown/yellow wire from the alternator being the rest of the circuit. Fairly easy to check this system, especially if you pull the speedometer or tachometer from the instrument pannel.

Les
Les Bengtson

This thread was discussed on 26/04/2006

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