I have just fitted a single ignition coil to
​​​​​​my 84 and I have a spare proper Marelli coil
Can this be used as a spare with a lucas dizzy, I have the wiring plug to convert.

 

Measure the primary resistance, spec for the CEI box is that the primary should be .6 ohms. Don’t know about mounting it.

 

What is CEI plz

 

Constant Energy Ignition; it was Lucas’ name for the system. Black AB14 module on the left intake manifold, with magnetic trigger inside distributor.

 

CEI is what you have. So you need .6 ohms if RGK is right, but I thought it was .5. Point is if it is significantly different from .5 or .6, don’t use it. I had an XJS with CEI and it just DEVOURED ignition amplifiers. I thought I was getting crappy Chinese ignition amps, but no, the problem was the coil ohm read was nowhere near spec. When I replaced the coil, the ignition amp never failed again. . A GM HEI amp (used inside the Lucas CEI ignition amp box) is like $50-$70, which isn’t worth risking compared with a coil.

 

I'm getting 00.6 on the marelli which works out at 00.4 when the lead resistance is subtracted. Would that be enough? Screen a bit melted.

 

Rex
Knowing nothing about Marelli ignition, I think the ohm rating will be OK, but you face another problem. I have a feeling the coil has two king leads to the dizzy? If I am right, these must be fired by separate signals from the Marelli system.
So (if I am right) the coil must be separated into two parts somehow, with each part running six cylinders - which we know is true because of the famous Marelli failure mode. This separation is the problem you face using it on a Lucas car, as one part of the Marelli coil will not fire 12 cylinders. The Lucas can only fire one coil, so I cannot see how you can use a Marelli coil in a standard Lucas system.

 

The Marelli system does use two coils.

I think the ohm reading is just fine. The only thing left to do is plug it in and find out. The worst case scenario you burn up a GMHEI module after some number of miles.

 

In which case it will run, but it will probably not run 12 cylinders above about 2500/3000 rpm because the recovery time will be insufficient. It will be the equivalent of running a single Lucas coil instead of the dual coil setup, pre-Ducellier coil appearing.
The Great Palm talks about this possibility and says an automatic coil selector might be a way round it; but that smacks of far too much complication for me! Also such devices are not designed to switch several thousand times a minute, rather to enable a single switch to a backup coil if one fails during a race, for example.

 

I actually purchased one of the aftermarket lookalike a marelli coils that are sold to replace 2 coil systems.but
1. I didn't like the fact it was so close to the dizzy and
2. I didn't like electrical connections on raised columns
I purchase a s/H marelli with a horizontal mount but the push on terminals are uncomfortably close to the small cross over vacuum pipe. I chect the resistance of the after market coil and the 2nd hand marelli and they were the same 00.5 ohms So I got a 4 pin plug wire up and it starts and runs ok. And to my eyes looks o/e as opposed to the anonymous after market one. We will see.. at the end of the day it's just a modern resin coil. 😊😊😊