Typewriters wrote:The term "skip fire" is curious; he makes it sound as if perhaps modern units with electronic fuel injection aren't injecting fuel to every cylinder on every power stroke when idling.
You basically got it right, it is in fact a fuel conversation feature when the engine is idling. If you figure that under normal conditions, every cylinder is firing for every two rotations of the crankshaft, the skip fire feature is firing the minimum number of cylinders necessary to keep the crankshaft turning. This feature when enabled will also draw the engine idle speed way down. Skip fire is only possible on engines with EFI, not on mechanical governor engines. I seem to remember skip fire only on HDL engines (AC6000's), but apparently that feature was cut in on FDL as well. Skip fire was only enabled when the engine was at idle speed and up to optimum operating temperature. In other words, if an engine was too cold, the engine would run at normal idle speed until it warmed up, and then cut over to skip fire. This was basically so that an engine would be "ready for the road" at all times when idling. As soon as you would move the throttle out of idle to notch 1, the engine would come out of the skip fire sequence and fire on all cylinders.