The timing to ignite the spark is more difficult to calculate during
cranking due to the engine crank acclerating and lack of a steady state.
To improve this situation, the spark can be ignited directly during
cranking using a trigger wheel position. This will give accurate advance
during the uneven cranking period.
During cranking, in Next Cylinder mode, the physical
location of the Trigger Angle directly fires the coil and determines
the timing. The time to start the coil charge is calculated and determined
from the Trigger Angle.
In This Cylinder
mode the Trigger Angle can not be used for timing spark directly. As
shown in waveform 2, the timing for spark is calculated just as it is
during normal running and will therefore be a bit less stable than that
of the Next Cylinder mode.
In the special case of waveform
3 the angle between Trigger Angle (falling edge) and Trigger Return
(rising edge) is 40º to 80º . When that condition is met,
the Trigger Return can be set in MegaTune to fire the spark The partial
settings below show a setting for This Cylinder mode with Trigger Return
for cranking timing. When using Trigger Return for Cranking Timing,
the Cranking advance Angle must be set to the Trigger Return angle for
use by MegaSquirt to set the start of charging the coil.