Federal

The fuel system consists of three major subsystems; a fuel storage system, a Feedback Carburetor with its supporting control system, and a fuel delivery and return system.

FUEL STORAGE
The fuel storage system consists of a fuel tank, a fill spout and filler cap. The filler caps primary function is as an evaporative emissions control device and is therefore covered in detail in EMISSION CONTROLS. The remaining components are covered in COMPONENT OPERATIONS.

Fig. 4 Feedback Carburetor Control System (Federal):

FEEDBACK CARBURETOR SYSTEM
The carburetor includes special design features to obtain optimum air/fuel mixtures during all engine operating modes. Fuel metering is accomplished through the use of two solenoid operated valves (Feedback and Slow cut solenoids) which add or reduce fuel to the engine as necessary. The activation of the valves is controlled by the length of time current is supplied to the solenoids. The solenoid valves operate at a fixed frequency. By varying the amount of time the solenoids are energized during each cycle (duty cycle), the air/fuel mixture delivered to the engine can be precisely controlled. The duty cycle to the solenoids is controlled by the electronic control unit (ECU) in response to signals received from various sensors. The primary difference between the California and Federal systems is in the vacuum sources used to control the high altitude compensation system (refer to EMISSION CONTROLS for further description of this secondary control system). For a more detailed description of the control of the feedback carburetor system, refer to COMPUTERIZED ENGINE CONTROLS.

FUEL DELIVERY AND RETURN
The fuel delivery components consist of fuel supply and delivery lines, a mechanical fuel pump and a fuel filter assembly. The Fuel return portion of the fuel system consist of lines and couplings and includes the vapor recovery system, therefore these are all addressed jointly under the heading of FUEL/VAPOR LINES. The function of the return line is to recover excess fuel vented from the fuel pump check valve (to relieve excess pump pressure) and return it (through the accelerator pump) to the fuel tank. The return line is a low pressure part of the fuel system.
The function of the vapor recovery lines are to provide a route for the recovery of fuel vapors (both from the fuel tank and the float bowl) either for storage in the charcoal canister, or for evacuation through the purge control system. Additionally contained in the vapor recovery system are two components, an overfill limiter and a fuel check valve. These components primary functions are as evaporative emissions control devices and as such are covered in detail in EMISSION CONTROLS.