Electronic ignition for the Citroën GS
About 18 years ago I got the chance to drive a GS estate with the semi automatic gearbox (c-matic). It was for sale at a Citroen specialist. The smooth and quiet ride impressed me greatly back then. I also remember when I looked under the hood, how engine oil covered the entire engine bay.
Since I own my GS, I have been wondering how to make it drive as smooth as possible. I have revised a part of my own GS-engine, and it runs very well, I started to look in to ways to optimise the performance. Not in a race-car kind of way, but in a smooth, quiet and economical one.
To replace the conventional ignition with mechanical advance by an electronic unit seemed a proper part to improve, since the ignition distributors can wear out and the vacuum advance mechanism can also be a bit tired since it works with a membrane in a capsule that almost always leaks after 30 to 40 years (I sometimes forget that all GS’s and GSA’s are pretty old cars nowadays)
What are the options for electronic ignition?
The 123 ignition system is a very good alternative for conventional mechanical ignition systems, because it replaces the whole contact points, condensor and – importantly– the mechanical advance system. There are many models available and they can be fitted very easily. The latest models even offer an app to control the whole ignition system via an app on your phone. Model the centrifugal and vacuum advance curve, adjust it while driving etc etc. Unfortunately no such unit is available for many old car makes and models, but not for the GS. I think that there are two reasons for this;. One; the GS is not a very common car and not worth very much on the market and two; there is a factory electronic ignition available….
Citroëns own electronic ignition from the GSA
The successor of the GS, the GSA was fitted with an electronic ignition system. But why not fit this on the GS then? The advance curves for the 1130 and 1300cc engines of the GSA are different than the values for my 1015cc GS engine. So it is possible, the car will run pretty good (I know of a few people who did it and are very pleased with it, but it doesnt result in the proper engine characteristiscs.
Buy: Online marketplaces like eBay and the known GS/GSA parts suppliers
Cost (approx): 100 euros for a good distributor, module. Excluding fitting by a mechanic if you can’t do it yourself
Existing distributor with Hall type sensor
Hall sensor in existing distributor; get rid of the points and condensor, but still have the centrifugal and vacuum advance system. A company in the north of holland offers such an option. Seems very solid, and not too expensive. A kind of in-between solution.
Buy: Sparcon
Cost (approx): 285 euros for a good distributor, module. Excluding fitting by a mechanic if you can’t do it yourself
Custom build distributor with 123-module
It took me a while to find a company that fits the famous 123-ignition module into a custom distributor. The main advantage is that most of the mechanical system is replaced by a electronic one that is configurable. I got in touch with the company that makes these custom units and they confirmed that they could fit the 123 into the Duccelier distributor for my GS. In fact, they had already done it a couple of times. So I ordered it, and waited. It arrived after two weeks and my impressions were that its very well made. It came with a new coil, distributor cap and rotor arm.
Buy: www.123ignition-conversions.nl
Cost (approx): between 500 and 600 euros
Installation
Fitting the new distributor
Fitting is easy. Remove the old coil, and fit the one supplied by 123 ignition conversions.
Unbolt the old distributor, remove the ht-leads and fit the new distributor. It comes with a rotor arm and a cap. Carefully put the ht-leads on the proper connections in the new cap. Then connect the wires with the correct connectors (not supplied). The manual is pretty clear; there’s a positive from the ignition, a negative to the bobine and a permanent negative. After fitting the wires the distributor has to be set at its static timing point. On all GS and GSA engines, that is 10 degrees before top dead center (TDC). On my GS you can rotate the crankshaft until the mark on the flywheel is exactly opposite the 10 degree mark on the flywheel. This can prove to be a challenge, because the oil dipstick is right in the way. But if you use a mirror or, in my case, take a picture with you mobile phone in the right position, you can achieve it. Then, the distributor can be rotated to position it so that the led in the unit just comes on. Watch out: for me it was not obvious that you have to remove the distributor cap to see the led; its in the 123 unit, so you have to look “backwards” in the distributor to see it light up. I also used my mobile phone in selfie setting this time.
Plotting the centrifugal and vacuum curves
In the Citroen manual, there are several advance curves printed. My car is a GS from 1974 with the 1015cc engine, and it is fitted with a Ducellier distributor with the GA5 advance curve and the GD4 vacuum module. So it was easy to look them up:
123 ignition provides a handy manual in which they explain how to read the curve in the workshop manual and how to convert it into a curve that the 123 understands. Key is that Citroen (and most other manufacturers) state the degrees of advance and rpm in distributor values. So to resolve them to crankshaft values, the values have to be multiplied by 2, because the camshaft on which the distributor is mounted, turns half as fast as the crankshaft. In this example the advance at for example 1250 rpm distributor degrees is 11,5 degrees. So the curve in the 123 should be 23 degrees at 2500 rpm. Of course it is; add 23 degrees to the static timing of 10 degrees before bdp and you end up with 33 degrees, which is exactly the value the Citroen mechanic back in the day (and mechanics who dare to work on GS's nowadays) had to use when checking the advance at 2500 rpm with the vacuum hose disconnected. So the points of the distributor advance curve for the 123 are as follows:
Centrifugal advance curve
| RPM | Advance |
|---|---|
| 1000 | 0 |
| 2000 | 20 |
| 2500 | 23 |
| 5000 | 33 |
But then there is also the vacuum advance, and this is a bit trickier to plot into the software of the 123. You have to define the points from the graph from Citroen, but then convert the points where the vacuum kicks in and flattens off from mmHG to KP. And then you have to convert the values from relative pressure to absolute pressure. It’s all clearly explained with several example curves in the manual.
It results in a vacuum advance setting of
| Pressure | Advance |
|---|---|
| 0 | 0 |
| 57 | 14 |
| 89 | 14 |
Experience so far
So far the car drives very well with the new ignition. It pulls well and the engine feels very smooth through all rpm’s. The fuel consumption has stayed the same but that could because I pushed the engine pretty hard to test the system and I also fitted new main jets in the carburator to better accommodate the modern fuel (which is not as good as before because of added ethanol). I experimented a bit with different vacuum curves and with tuning the ignition while driving. It was pretty hard to notice the small steps you can adjust via the tune option. The engine response it only noticeable when retarding too much, and with the current curve, I couldn’t get it to pink. I am very happy with the result. After a few thousand km’s I will get back to write a small update.
You are right
Before you accuse me of butchering my GS with unnecessary stuff and depriving it from its originality and telling me this conversion serves no purpose because a GS runs fine on its traditional ignition setup…. You are right in that a GS can run very, very well with the original system that was fitted to it 40 years ago.
No. Problem. At. All.
But the chance is that not all parts are in the best shape they were when the car left the factory. I don’t mind changing ignition contact breaker points and condensors at all. If you can find good original quality parts. Parts like vacuum units, that have significant effect on ignition timing become harder to find new and used ones almost always leak.But more importantly, who has a Surieaux test machine available to test all components of the system and adjust it if necessary? Almost no-one. I don’t. And I admin that I am a sucker for using new technology to improve my old cars with as much respect to the original designs and ideas as possible.
So you are right, I am probably waisting my time and money. But I find it a pretty fun time to waste. Drive them old Citroëns!
