FUEL PRESSURE CONTROLLER FOR INTERNAL COMBUSTION ENGINE

PURPOSE:To prevent an unstable idling state and an engine stall from occurring, by having control pressure to be led into a pressure regulator when output of an air-fuel ratio sensor is selected from lean to rich at the time of high temperature starting, duty-controlled by a negative pressure control valve. CONSTITUTION:In the case where vapor is generated in a fuel system at the time of high temperature starting, if an output signal out of an oxygen sensor 16 is a lean signal, a duty ratio of a negative pressure control valve VSV15 is set to 100% by a command out of a control circuit 11 and control pressure to be led into a diaphragm chamber of a pressure regulator 12 is set to atmo spheric pressure. And, when output of the oxygen sensor 16 is selected from a lean signal to a rich signal, from that point of time, the duty ratio of the VSV15 is made so as to be lowered from the 100% by degrees, and when then the specified time elapses, the duty ratio is set to 0%. With this constitution, fuel pressure is gradually lowered from the high pressure side to the low pres sure side so that a large variation in the air-fuel ratio is avoided.