A distributorless ignition system
Electronic advance control greatly improve ignition advance as it eliminates the need for bob weights and rotating plates. In fact, electronic engine management completely eliminates the need for a distributor and, with it, the distributor cap! The distributor cap is a major problem on high revving race cars when you increase the spark plug gap and the secondary ignition voltage. With higher voltages and bigger spark plug gaps, flash over, or cross firing, is more likely, especially between adjacent terminal posts in the distributor cap. And the terminals posts in the distributor are even close together when your engine has eight or more cylinders.
When you eliminate the distributor, you need another system to generate a signal for the engine control unit (ECU) to know when each piston reaches top dead center (TDC). This can be accomplished by taking a signal from a pulse generator attached to either the front pulley on the crankshaft, or the circumference of the flywheel. The ECU can then use this signal to determine the correct ignition timing and advance firing angle for each cylinder, and can switch the low voltage primary circuit on and off at the correct moment.
The important thing on a distributorless ignition system is to ensure that the pulse trigger is correctly mounted. This actually entails three things you need to check: the firing pin diameter, the firing pin position, and the air gap.
The Firing Pin
The firing pins must be precisely positioned and must be of the correct diameter. Obviously, for accurate timing, the firing pins must be accurately aligned with the magnetic pick-up when each piston reaches TDC. To get a reliable signal, the firing pins must be of the same diameter are the magnetic pick-up. Using a larger or smaller diameter firing pin than the magnetic pick-up will lead to inaccurate signal generation, and inaccurate ignition timing! The result could be catastrophic!
The Air Gap
The air gap between the firing pin and the magnetic pick-up must also be adjusted to the gap specified to by the manufacturer of the distributorless ignition system. Most manufacturers specify an air gap of 0.020-0.040". If the air gap is too large, the signal will be too weak and will result in miss firing and lack of power. If the air gap is too small, the signal may be generate too soon and your ignition timing will also be out.