Which coil to use with Lumenition ignition module

South Gippy Rover

South Gippy Rover

Active Member
Hi All,

My 1975 3500S has Lumenition electronic ignition fitted.
It is currently fitted with a Bosch GT40R which has died.

When I went to buy a new one, the guy in the shop (who seemed very knowledgeable) said the car needs a plain ignition coil with no ballast resistor required, as there is an aftermarket electronic ignition fitted.

I have googled it and found this:

"The Standard Optronic system is ideal for all road and classic cars up to and including 8 cylinder engines with a special version for boat engines.
The recommended ignition coils are the Lumenition MegaSpark 4 coil-and-ballast-resistor combination or the MegaSpark 6 unballasted 3 Ohm coil. "


Now I am even more confused as both types are recommended.

Thanks in advance.

Paul
 
Hi Paul,

There are two types of Lumenition systems. The standard system uses a ballasted coil, the Bosch GT40R being one such type. For the standard system, the coil must have a primary resistance of between 1.2 and 1.4 ohms. A ballast resistor must be used, else the power module will be damaged. The sports system comes with a 12 volt coil and does not use a ballast resistor. The power modules are different, the latter is black instead of silver.

Ron.
 
Hi Ron,

Thank you for the info.
Mine has the standard silver module. I'm now guessing that i should replace the coil like for like.
From reading previous posts, I understand that the ballast resistor is a wire which I assume that this is still in place.
I will get the same coil and see how it goes.

Thanks again.

Paul.
 
Pleasure Paul.

When you connect your new coil, with the engine idling, you should see approximately 10 V at the coil. If you see closer to 12, that would suggest the ballast resistor has been bypassed. That might suggest why your coil has failed, but then if that we the case, then the power module would likely have also been damaged.

Ron.
 
hi there,
Has anyone fitted the Pertronix system with a new coil, a friend recommended it to me as part of the solution to make my car easier to start.
I checked my coil and on the bottom it has the date of 1975, my car is a 1976.

Peter
 
Hi Peter,

I am still using my Rover's original factory fitted Lucas coil, date stamped 1973. With 357,142 miles (575,000km) on it and still running strong, the engine starts very easily. I am using Lumenition, a truly excellent system.

Are you still using points?

Ron.
 
ButterFingers said:
No its a Rover...:rolleyes:
but, it starts like a Delorean, 5 mins with "start you bastard" yellow can one, lots of choke, several "Damms and S you B" and I am away into town.... :)

Peter
Click to expand...

So what you are saying is that your car is actually an educational aid..... extending your vocabulary. :D
 
ghce said:
So what you are saying is that your car is actually an educational aid..... extending your vocabulary. :D
Click to expand...

Yes, I now include the letters A ,E I,O U, in every word I create, Rover has 2 ....:p
it has something to do with having a coil made one year before the birth of my car, back to the future, to Coil a phrase...

Peter
 
Hi Guys,

Ron,
I have just purchased a Bosch coil (SU12R) for use with ballast resistors. It's primary resistance is reading on the workbench is 3 ohms.
The coil I am replacing is a Bosch GT40R. It's primary resistance measures 2.8 ohms. (Secondary resistance is open circuit).

These are obviously higher than the specs mentioned.

If the original GT40R coil was working OK with its primary resistance at 2.8 ohms is it worth the risk of fitting the new coil or do I definitely need a lower resistance coil?
Your knowledge/advice is greatly appreciated, especially if anyone can recommend a coil with the appropriate primary resistance.

Thanks again,

Paul.
 
Hi All,

Done some more googling and found this.

Lumenition coil.jpg

I have highlighted in red the paragraph of interest.
Ron, with regards to the primary resistance of 1.2 - 1.4 ohms (as per the workshop manual), I assume that this is a standard applicable to the original Lucas coil.
My question now is that if the Lumenition set up needs a coil with resistance of around 3.0 ohms how does the ballast resistive wire affect things with my recently purchased (but yet to be fitted) 3.0 ohms coil.
Is the wire a known resistance? (That would be too easy!).

I suspect I am over analyzing this and should just fit the coil and see what happens, but am open to help and advice in case there's a chance I fry the Lumenition module.

Cheers,

Paul.
 
Hi Paul,

There is something strange here. I too have a Bosch GT40R coil, that I always carry as a spare. The primary resistance when measured between the positive and negative terminals is 1.3 ohms. I did some research before I purchased it, which was many years ago, and the information that I obtained was...Primary resistance 1.25 - 1.35 ohms. Primary turns - 240. Secondary resistance - 8 - 10,000 ohms. Secondary turns - 24500. Output 29.1 kV @ 100Hz. Peak current 3.7 A. Requires 9 V supply, with ballast resistor of 1.8 ohms.

According to the paperwork that I have for my Lumenition kit, the power module is suitable for coils or coil/ballast combinations of not less than 3 ohms. The factory fitted Lucas 16C6 ignition coil has a primary resistance of 1.4 ohms.

From my way of thinking, a coil with a primary resistance of 3 ohms is typically a 12 volt coil, and thus not meant to be used with a ballast resistor. The attached pdf file from Bosch shows the primary resistance of both the GT40R and SU12R to be 1.3 ohms plus or minus 10%.

http://apps.bosch.com.au/AAExtranet_TechSearch/docs/GeneralInformation/BICCoilspecifications.pdf

Ron.
 
Paul, my original Lumenition module that I installed in 1991 worked until 2015, when it started to misbehave. I replaced it with another module, and everything works perfect again. I am still using the original Lucas coil, 1.4 ohm primary resistance with the ballast resistor. If you use a 3 ohm call with a ballast resistor, the current supplied to your call will be markedly reduced, to a quarter of what it would be with 1.4 ohm coil.

Ron.
 
Hi Ron,
Things get slightly more complicated.
I found this link on a triumph forum.

Note: this information in this video is possibly incomplete/incorrect.


With regards to your second post on Tuesday, with the ignition on but engine obviously still not running, my positive terminal on the coil reads 12.3 volts.
I now suspect my ballast resistor has been bypassed.

Interesting enough, with the ignition completely off there is still 0.15 volts at the positive terminal.

I am now thinking that I need to fit a 1.5 ohm coil with an additional 1.5 ohm ballast resistor.

I have remeasured the primary resistance on my new SU12R coil with a decent multimeter and it reads 2.0 ohms as opposed to the 3.0 with el cheapo multimeter I used earlier.

Thanks again,

Paul.
 
Last edited:
Hmmm, I would have thought that there should be zero volts at the ignition switch when it is switched off.

It definitely sounds like the ballast resistor has been bypassed, if you have 12.3 volts on the coil with the engine off. Fitting a ballast resistor with your new coil sounds like a good idea Paul!

Ron.
 
Hi all,

After 5 hours on my car today, time for a final update before I put this post to bed.
The YouTube clip above is not quite correct.

I have found a Lumenition technical bulletin which details the process more thoroughly. There is a final step which is to remove the wire from the negative coil terminal and then using a different length of wire connect the negative coil terminal to earth. If there is a ballast resistor then the voltage will drop to approximately 6 volts when the negative terminal is earthed.

This does indeed happen on my car so I do have a ballast resistor.

The new coil I bought is a suitable replacement for the dead one with regards to primary resistance.
I installed the new coil and................
nothing!!!!!!!!!

Still some progress has been made.

On further investigation there is no power supply to the Lumenition ignition module with the ignition turned on.
In addition, I already know that my aftermarket electronic fuel pump does not pump any fuel. (See my post in V8 engine). I have traced the power supply wire from the Lumenition module and found that it is spliced from the power supply to the fuel pump.

I have no power to either the fuel pump or the Lumenition module.
To be continued.....
 
You must log in or register to reply here.
Back
Top