In an engine control system, an accelerating condition is detected from the phase
of a crankshaft and an induction air pressure. A stroke condition is detected from
a rotational angle of the crankshaft and an induction air pressure. A differential
pressure between induction pipe pressures detected at a predetermined crank angle
on an exhaust stroke and an induction stroke and induction pipe pressures resulting
at the same crank angle on the same strokes is calculated as an induction air pressure
difference PA-MAN. When PA-MAN is equal to
or larger than the threshold, an accelerating condition is determined to be occurring,
and fuel in acceleration is immediately added to a steady-state fuel injection
amount for injection. To improve accelerating condition and the induction air amount
detection accuracy, a volume from a throttle valve to an induction port is made
equal to or smaller than the volume of the stroke of a cylinder.
