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MG MGB Technical - MGB electronic coil

l have and electronic lucas 45d distributor with a Lucas DLB105 sports coil puchased from "Seller info
simonbbc ( 2137) 99.8% " on ebay.

The car runs ok but is difficult to start. Have just established that the Lucas coil has a very low spark.

Any idea what the equivilent coil would be in Bosch. The Lucas coil is non ballast.

R W Pope

What model is your car? Aus built or later US import.
If its a local its 12V and you use a "Bosch Blue" coil

The car is an MGB GT 1969 and it was an American import.

R W Pope

Rick I an not sure when the US cars went to the ballast system but you could try running a 12V jumper wire from the fuse box to see if it improves your existing coil. If it does make it permanent. I think the Bosch Blue would be the right replacement.


Thanks for the help, purchased a new 12v, non ballast electronic champion coil today from repco. Also the person l purchased th dissy and coil from in the UK is sending out a new coil free of charge.

Got the car to fire today but timing and perhaps an earth leak are a problem. Will ship back to Ballarat via RACV tomorrow and perhaps get better help than here in Ararat.

R W Pope

Rick. The coil designed to operate at a full time 12V input will have a resistance of about 3.65 ohms when measured from the input (switch) terminal to the output (distributor) terminal. The coils designed to operate at reduced voltages (12 V use external resistor) will have about 1.5 ohms resistance when measured in the same manner.

Your MGB could be either a North American Specification (commonly called a "US spec" or "49 state spec") or a California specification vehicle. Most of the differences were because California required additional emissions control equipment that the Federal government did not yet require. However, in 1969 any differences between the two specifications would be minimal.

All of the North American/California specification cars used an ignition system designed to operate at a full 12 volts up until 1975. So, you car was sent out with a coil designed to operate, full time, at 12 volts input and that is the type of coil you should use.

Please be aware that "the Lucas coil has a very low spark" does not, always, indicate a problem with the coil itself. A problem anywhere in the low tension circuit can cause the coil to demonstrate a weak spark.

In addition, the coil can be putting out a strong spark but, if the coil lead (king lead) is bad you will see a weak spark at the end of the coil lead.

I do not know what particular form of Lucas Electronic Ignition you have purchased. Two were used with the MGB, the Lucas 45DE4 (Opus) and the Lucas 45DM4 (CEI) systems. The 45DM4 looks like the more commonly found distributor having a circular body. It is the "good" one to have. The 45DE4, often referred to as the "Opless" system has a round body with a rectangular box grafted onto the side. These did not hold up well and I have not seen an actual working 45DE4 since mine went out in the first three months of ownership on a 79 B purchased new. Replaced with the CEI system under factory warranty.

Hope this will provide you with some useful information.

Les Bengtson

Les: The other cool fact - the Lucas CEI is actually a GM HEI ignition. If you take the back off of the CEI module that is located under the coil, you will find a 4-pin HEI module. I recently installed a CEI ignition in my ZA Magnette with a Pertronix 4-pin HEI uprated module and their 50,000 volt coil - the car starts almost before it has completed a full revolution!
John Perkins

This thread was discussed between 02/09/2009 and 03/09/2009

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