Fuel Delivery Operation
Fuel is supplied to the fuel rail assembly, mounted on the intake manifold, by an in-tank electric fuel pump. A constant system pressure of about 36 psi (2.5 kg/cm2 ) is maintained by the pressure regulator. The regulator is mounted on the intake manifold chamber in line with the fuel return line. It contains a spring controlled diaphragm which is exposed to fuel pressure on 1 side and intake manifold pressure on the other. Fuel delivered in excess of that required to maintain system pressure is bypassed by the regulator and returned to the fuel tank via the fuel return line.
Fuel is supplied to the intake manifold from the fuel rail assembly, through the fuel injectors. The injectors are electro- magnetic solenoid valves. A needle valve in the injector is held against a seat by a coiled spring. An electrical armature at the back of the valve reacts to electrical signals from the ECU by pulling the injector needle off its seat. This allows fuel to be injected into the intake manifold. Since fuel pressure is maintained at a constant level, the amount of fuel injected is dependent only upon the length of time that the injector is held open (injector "ON" time). All injectors are fired simultaneously, twice per engine revolution.
During starter engagement, with cold engine, additional fuel is supplied by the cold start injector. Power to the injector is routed through the coolant temperature thermo time switch, mounted in the water jacket of the cylinder head. The switch contains an electrical contact on the end of a bimetallic strip. When the engine is cold, the contact is closed and power to the injector is supplied. The switch maintains power to the injector for a maximum of 8 seconds at a coolant temperature of -4°F (-20°C). At 95°F (35°C), power to the injector is cut off.