Fuel injection control system for an internal combustion engine

A fuel injection control system for an internal combustion engine in which fuel delivered from a low pressure fuel pump is pressurized by a high pressure fuel pump and is supplied to a fuel injection valve, said system comprising:

• a pressure sensor to detect a pressure of fuel between said high pressure fuel pump and said fuel injection valve;
• a high pressure fuel pump control unit configured to carry out proportional plus integral control of said high pressure fuel pump so that a detected value of said pressure sensor comes close to a target value;
• a low pressure fuel pump control unit configured to decrease a feed pressure, which is a pressure of fuel between said low pressure fuel pump and said high pressure fuel pump, when said high pressure fuel pump is in operation and when an integral term in said proportional plus integral control does not change or is decreasing, and to raise said feed pressure when said high pressure fuel pump is in operation and when said integral term is increasing;
• and
• a feed pressure increasing unit configured to make said feed pressure higher when said high pressure fuel pump is in a stopped state than before said high pressure fuel pump is stopped.