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 using a crankshaft position sensor that takes a signal from a pulse generator attached to the front pulley on the crankshaft, the pully on the camshaft, 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.
Crankshaft Poisition Sensor
There are different types of crankshaft position sensors available. The most common is the hall effect crank position sensor that reads a notched metal "interrupter" ring on the back of the crank pulley. This system also uses a separate cam position sensor in place of the original distributor to allow the ECU to determine the correct firing sequence which it then uses to control both injector and ignition timing. A siliar system, called the combination sensor, uses two hall effect sensors and two notched interrupter rings on the back of the crank pulley. The one interrupter ring has a single notch for rpm and ignition timing signals, while the other has three notches for six-cylinder engines, or four notches for eight-cylinder engines. This generates signals that the ECU uses to determine the correct firing sequence.
Another type of crankshaft position sensor is the magnetic pickup that reads slots machined in a "reluctor" ring in the center of the crankshaft, on the crank pulley or flywheel. The reluctor ring has several slots that generate signals that the ECU uses to determine the proper ignition and injector timing.
The important thing on these distributorless ignition systems is to ensure that the crankshaft position sensor 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.