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MG MGB Technical - Lumenition 'Optronic' Ignition System

Posted 20 August 2012 at 14:44:02 UK time

Can anybody help?

(MGB 1980. Std 1800cc engine)

The car starts and runs ok when cold but after some 10/20 miles starts to run a bit rough and when I stop the engine it won’t start again. It’s an ignition problem as I have a very weak spark at this point stopping the engine starting but when it does start the park is then good and strong.

Leave the car to cool down and it starts ok and runs no problem. Get the engine hot and the problem reoccurs.

I’m suspecting the coil but having had the problem for some time now I have progressively changed the entire ignition system and can’t put the fault down to any one component.

I have a Lumenition ‘Optronic’ ignition system installed with MS4 High Energy coil. (I guess I’ve done some 5k miles with the original system since installation but the original is now all replaced). The coil is getting very hot when running and then won’t restart, but when cold all is ok.

I suspect the coil is breaking down with heat and is also affected by the heat of the engine but the coil is new (I’ve also tried a standard coil as well as the high output Optronic coil). Dis cap, leads and rotor arm also replaced.

The Optronic high output coil runs with a resistor. Can anybody confirm the voltages either side of the resistor? I’m getting 13.9v the input side (battery) and 9.4v output (coil side). Are these correct or is a high battery side output voltage ‘cooking’ the coil. It’s not the resistor at fault as I’ve changed this as well. Is the 13.9v input high?

Any thoughts anybody as I’m completely stuck.

Thanks

Brian
Brian Davis

Brian, check whether you have a ballast ignition sysyem.
I've read diverse places on the net that using a so called 'high energy' coil with a ballast system is not good! I also have a rubber bumper model (77 roadster) with a 45D dis. Just bought the cheap accuspark module to try it out. I was informed to make sure which system I had - non balast/ballast. Now I have to find where the ballast wire is so I noticed your thread and the high energy coil...hope my comments help

/Moss
Moss

I forgot to mention that one should check for ohms! Ballast system at 1.5 ohms - non-balast at 3 ohms or there abouts, the point being there is a difference.
Moss

Brian
I'm sure there are many contributors who can help and I've read your post a few times in an attempt to give some guidance. However, the more I read the more confused I get on what you have and have not done so far. I (and a few others on here) need a bit of structure and clarity to help with troubleshooting.
Can I ask you to start at the beginning and catalog the changes made so far (in order of doing them..).

Also, to answer your specific questions

1, "can anyone confirm the voltages either side of the resistor" No not without knowing the resistance of both. Measure the resistance and post the values. From those we can work out the voltage to expect and the average current being drawn by the coil. Are you measuring the voltage with the car running?
2, "13.9v battery size" Again I'M guessing the car is running and you are actually measuring the alternator output voltage. It's not excessively high and is unlikely to fry the coil with a resistor in series to limit the current in the coil and remember the ignition system actually "switches" the current off between sparks.
You'll need to document how the ignition system is installed to confirm it's as Lumenition intended.

If memory serves me I seem to remember that there has been issues with the optical unit in the dissy being effected by heat. But you'll need to research this on the web.

Good Luck

MGmike



M McAndrew

Have you tried a Distributor Doctor rotor arm? Many replacement arms can short out when hot yet run fine when cool.

Engine running battery voltage 13.8-14.3, 9.4 sounds about right. Cranking voltage on coil should be full battery voltage.

Coils do run hot and the high power coils run hotter still.


Peter
Peter Burgess Tuning

An update.

Hopefully I've solved the problem. (Well stumbled into a solution).

I changed the coil from the Optronic high energy coil (with resistor) back to the original standard coil and wiring configuration. It's being running OK since then.

It was not a problem with a faulty HE coil or resistor as both were changed for new ones (an expensive job with the coils costing £35 each). It must be something to do with matching the LT voltage input into the coil (through the resistor) with the coil performance as the problem was that the coil was breaking down when hot and restricting the spark, hence the problem with running rough and hot starting. Has anybody got any ideas?

I did around 60 miles fingers crossed testing with the standard coil and all went OK. I then took the car on the Coventry Festival of Motoring car run on Sunday, 60 miles of faultless driving.

The new venue for the Festival (Stoneleigh Park, near Kenilworth, Warwickshire) was excellent as was the festival organisation.

Hopefully a problem now fully solved.

Brian
Brian Davis

This thread was discussed between 21/08/2012 and 27/08/2012

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