Advance and retard are accomplished in the following ways (figure 5-21).
• In advance mode, the stepper motor arm retracts in steps. This causes the pivot shaft to rotate.
As it does, it swings the paddle-like control lever away from the servo valve. Spring pressure pushes the valve off the advance passage. Pressurized fuel enters the advance passage and pushes the advance piston in the advance direction.
• In retard mode, the stepper motor arm extends downward. This rotates the pivot shaft in the other direction, causing the control lever to press on the servo valve to overcome spring pressure. The valve opens the drain passages, but blocks the advance passage. The lack of pressure at the piston causes it to move in the retard position direction.
