Lumenition electronic ignition

[Elan4James]

Just completed rebuild of Plus2 after 30 +years off road. Engine rebuilt but using original Lumenition ignition. Engine starts easily and idles smoothly, but runs roughly when driven.Coil gets very hot. Coil resistance is 2.8 ohms voltage across coil with ignition on and engine not running is 9.5volts. Is this correct or should it be 12volts?
Testing Lumenition module and sensor as per instruction leaflet gives a good spark and voltages across 3 wire connector are correct.
Any thoughts on why coil is so hot and voltage across coil is only 9.5 volts

[draenog]

What date is your plus 2? It sounds like you may have a ballast resistor fitted.

Originally the coil would have been fed 12v when running and during starting. However, the starter motor takes so much current the battery voltage drops, reducing the coil output. To solve this, a 9v coil was fitted. To prevent the coil receiving 12v once running, the coil is fed via a resistor, which reduces the voltage from 12v to 9v. You should be able to tell by looking at the coil wiring. If a ballast is fitted you will have two positive feeds (one from the ignition switch and one from the solonoid) and somewhere there will be the resistor.

A very hot coil may indicate that it is failing (shorting internally). When I had this, I had problems starting when hot and misfiring at high RPM which was fixed by a new coil...

Search on here for "ballast resistor". There's lots of posts on the subject

[Elan4James]

It's a 1972 plus 2 s130. Coil has two terminals and no ballast resistor. The voltage at the Coil is about 9.5v with the Luminition (which was OK 30 years ago).This means the Luminition is taking 2.5v when the engine is not running,which doesn't sound right. I think I'll have to revert to points and condenser and to see if that solves the issue

[Craven]

Just had a quick measure for you same system as yours. In non running state, as I would expect about 1 volt across the unit. That is voltage on the switched side of the coil about 1volt. Maybe your test are not good.

[Elan4James]

Thanks for doing that. I think that as I've got 2.5 volts across the module it must be drawing too much and has an internal fault

[Craven]

If you have a ~ 3 ohm coil and you have 9.5 voltage drop across it suggests the static DC current of ~ 3 amps which is below a normal estimated value. Ensure the Lumenition unit has a very good low resistance path of earth return.

[2cams70]

I think I'll have to revert to points and condenser and to see if that solves the issue

Your mind is now firing on all cylinders.

[Elan4James]

Yes the Luminition module has.a dedicated wire back to a good earth

[Craven]

Quote Lumenition.
Fit power module using self-tapping screws supplied and placing eyelet
of short black wire beneath one screw head as earth, tighten down
securely ensuring a good earth. With fibre glass bodied cars run a heavy
duty earth wire or braid from mounting screw of power module direct to
the battery negative terminal or good earth.

[Elan4James]

Yes I have done that exactly as the instructions say

[TonyA]

I attach a diagram from my notes on my 1971 plus2 S130 which shows the coil with ballast resistor arrangement: where is 12V , where is 9V and the resistance readings of coil and resistor. And the cable colours. ..Hope it helps..Tony

[Hawksfield]

James
If your car has no ballast resistor and 2.8 ohms coil then the volt drop is correct at 9.5v with lumenition.
As for hot coil if you think the temp is excessive try a new coil. is it excessive while running. As they get very hot if u leave it on while static.
John

Good luck

[Elan4James]

Thanks for the information on the voltage drop. The coil is very hot after 10 minutes driving,and the Luminition module is as well although it is on a metal heatsink. Am reverting to points and condenser to see if that helps.

[Hawksfield]

James
The hot coil is your clue to a problem. The load you are suggesting is not.
Clear the obvious first.
John

[TonyA]

When my coil was overheating, I replaced it with a Remax ES4B coil from the Green Spark Plug Company: weighty and dense, not like the light, sloshy Chinese Bosch and Lucas labelled stuff. Three years on, still stays cool. Mine goes with an external ballast resistor; there is also an analogous model for the plain vanilla coil.

https://www.ebay.co.uk/itm/234856082597 ... media=COPY

Relocate the coil from below the airbox for fuel fire safety and make sure the case/ bracket has an earth strap.

Tony