Bosch 203 Modules

[Kevin Black]

I have a question about Bosch 203 modules. I don't use modules and I don't often tune normally aspirated cars so I could use some input.

BMW 6 cyl, 13-1 Compression, COP Coils, 2x203 modules.

I am diagnosing this from 250 miles away so logs are what I have to work with for now.
The engine is breaking up and showing lean like ignition misfiring.

They are only running 1.4-1.5 ms of dwell time, is this enough on a 13-1 NA engine?
Or, perhaps are they trying to save the modules (circuit racing application) from overheating?

They are on their 3rd set of modules, they could (should) have bought a CDI by now!

So the arguement to go CDI should be a fairly easy one,(they just want the car to run) - I just want to know what the potential of that setup is.

[MRMRacing]

The Bosch shouldn fail with proper setup and the right cooling. They must be mounted at a good cool surface. My old test car Volvo 960 had two 203 modules as stock. I used the Sm4 for long time without problems. This dwell table is almost same as stock ECU used for the stock Denso coils.

[MRMRacing]

This is how the stock install looks, in front of manifold the other modul. They are mounted here so the cold air is cooling the modules.

[Wroom]

Roberts table is what normally can be expected to work.

But some high current coils require a maximum of about 1.5 ms timing, or otherwise the coils burn.
As a contrast, Audi coil on top requieres at least 4.5 ms to give a good spark.
Just wanted to make the point that there is a great difference between different coils.

But since you say they are on their third set of modules, and on that low dwell time, i would suspect that the modules are not mounted so they get enough cooling.

The modules must be mounted of a very large metal surface that keeps its cool in all situations. Below 55 degrees celsius.
I have found that it can sometimes be near impossible to achieve this on a racecar. Especially in endurance racing.

Ignition modules are prone for problems.
Problem is that the efficiency of the driver transistor is inversely proportional to the temperature.
That is, "The hotter they are, the more heat they produce".

If mounted to hot they just meltdown. And if you have a bunch of them on the same cooling surface and one of them aren't getting enough cooling, (maybe to much coil current?), then it will overheat all the modules mounted next to it and so on.

For racing purposes the CDI solution is payed off on the first race that did not end in the pit because of problems with ignition.

My suggestion is to forget about ignition modules, and instead use a 500R CDI to drive the coils two by two.

If the engine revs high then forget about dwell ignition, since the max possible dwell time will be to low.

On a six cylinder four stroke engine, the max achievable dwell time for a certain rpm will be:
rpm ms
3000 6.7
4000 5.0
5000 4.0
6000 3.3
7000 2.9
8000 2.5
9000 2.2This is true for ignition modules like the 203's that require the ECU to set the dwell time.

There are ignition modules that handle dwell time internally, so called smart ignition modules, that can handle longer dwell times than those in the table above.
But don't be tempted to use those. Because when they get overheated they will first start to release ignition to early, and after some more overheating they will give out spurious ignition. And if that does not kill a race engine quickly...

So the only real good and reliable solution is to use multipoint CDI. Like the Autronic 500R.

[MRMRacing]

My table may be little to much for BMW and as Johan wrote some other coils will melt long before 2 mS. Some Nissan will not take any more than 1.8 mS, I am not sure for the BMW.

If going for the CDI remember that also the CDI needs a "cool" place. If mounting it away from the engine try to buy twisted pair wires for the coils and for the power to the CDI. I now keep them in stock because they are ultimate for noise supression.

To meet some regions EMC standards use of shielde twisted pair with the shield connected to ground at one end only, is a must. This is also the best alternative when going for a superior installation.