Fuel Injection Pump
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The fuel injection pump is a mechanical high pressure pump. The fuel injection pump is located below the intake manifold. Fuel is pumped to the fuel rails at a specified pressure. Fuel pressure is regulated by a valve on the inlet of the fuel pump, controlled by the ECM. Excess fuel from the fuel injection pump returns to the fuel tank through the fuel return pipe and a fuel cooler.
On vehicles equipped with dual fuel tanks, an electric transfer fuel pump is located on the left frame rail. This fuel pump is powered by the fuel pump relay that is controlled by the ECM. Fuel is transferred from auxiliary fuel tank to primary fuel tank in order to ensure all of the usable fuel volume is available to the fuel injection pump.