Ignition II

To find out the exact moment the spark has to be fired, the calculator must know in which position the crankshaft is. According to the previously defined TDC, a sensor captures the exact position. A toothed wheel on the crankshaft gives the information via 36 teeth, one tooth is missing for synchronisation.

Furthermore, a potentiometer captures the position of the throttle axis to determine the load. This can also be done by vaccum, but on my car the intake manifold wasn't equipped.

Crank position and load are then evaluated by the calculator.

 

This calculator in particular works together with the Ford EDIS ignition module, which fires the ignition coils. The picture shows both the EDIS and the coilpack prior to complete wiring.

This is it for the hardware (well... high tension leads and spark plugs are common to almost every ignition system). My next post will show what a map looks like and what it does to alter advance.

Cheers.

Ignition I

Animated GIF "borrowed" from mediaculture-online.
As you can see, the spark has to be fired just before the piston goes down, the highest point being called TDC (top dead center). This is commonly known as ignition advance. It is calculated in degrees as part of one 360° revolution of the crankshaft. An advance timing of 10° therefore means that the spark is fired 10° before TDC. As the engine runs faster and faster, the spark must be fired even earlier.
Complicated? You have to decide for yourself, normally - in older cars - a mechanical distributor does it for you. The down side is that mechanical advance is limited and you cannot have the full advance when revving high, i.e. you cannot take full profit out of the engine's potential power. With 3D electronic ignition you can do so, that's why I modified the ignition system on my car.
I opted for a system called Megajolt. It's a calculator you have to feed with some information (position of the crankshaft, position of the throttle axis of the carburettor or injection throttle body) depending on your car's specs. In return it fires the coils at the right moment and ignites the sparks. It's fully programmable and has free access. Megajolt can do a lot more but you can have a look for yourself at the installation guide .
One of the interesting things is to find out where exactly the TDC is. I manufactured a tool to find it which you can see here:

It is a dial gauge I mounted on an adapter I can screw into the spark plug thread. With the piston coming up, the gauge turns one direction (wrench on crankshaft - manual cranking without ignition!). The exact moment it turns the other way around, the piston goes down again. This method is quite precise.
Next 'episode'  will show the sensors and electronic components.
Cheers.