Fuel Delivery and Air Induction: Description and Operation

DIGIFANT FUEL INJECTION SYSTEM
The Digifant Engine Management System combines the engine's ignition and fuel injection functions into one system, managed by a single electronic control unit (Digifant Control Unit). With the Digifant system, basic fuel metering is determined by engine rpm and by the volume, pressure and temperature of the air entering the engine. The Digifant Control Unit receives air flow volume and temperature data from the CO Potentiometer, the air pressure data is supplied by a hose connected to the intake manifold which leads to a Manifold Pressure Sensor inside the Digifant Control Unit. The engine rpm data comes from the ignition system. The fuel is distributed to the engine through electrically-operated solenoid valve Fuel Injectors.

Four Fuel Injectors, one for each cylinder, are triggered simultaneously at a rate that is proportional to engine rpm. Fuel mixture is controlled by the length of the electrical impulse from the Digifant Control Unit to the Fuel Injectors, or the length of time that the Fuel Injectors stay open. The Fuel Injectors are mounted to a common fuel supply, called the Fuel Rail. Fuel pressure in the Fuel Rail is regulated to a constant pressure by a Fuel Pressure Regulator mounted to the downstream end of the Fuel Rail. An electric Fuel Pump feeds filtered fuel to the Fuel Rail, the Fuel Pump is mounted inside the Fuel Tank and the Fuel Filter is located under the car.

The Digifant Control Unit makes additional adjustments to the amount of fuel delivered by the Fuel Injectors based on input from various sensors. The oxygen sensor system provides the Digifant Control Unit with information on engine combustion efficiency by measuring the amount of oxygen in the exhaust stream. Two throttle switches on the throttle valve inform the Digifant Control Unit when the throttle is fully open or fully closed (at idle). A coolant temperature sensor provides the Digifant Control Unit with engine coolant temperature information for adjustments it will make during starting and warm-up.

In order for the Digifant Fuel Injection System to operate properly, the basic adjustments to idle speed, ignition timing, idle air/fuel mixture and throttle switches must be correct. If these basic settings are faulty or slightly misadjusted, the Digifant system will compensate for any differances or misadjustment, this can lead to incorrect or misleading test results. These basic settings are all related and all adjustments should be made together to insure proper engine performance and combustion efficiency. For detailed information and testing procedures of electronically controlled components of this system refer to COMPUTERIZED ENGINE CONTROLS.

FUEL PUMP AFTER-RUN SYSTEM
The purpose of the fuel pump after-run system is to reduce the chances of the fuel vaporizing, (boiling) in the fuel rail when under hood temperatures are high.

To prevent fuel vaporizing the fuel pump is used to recirculate the fuel. The pump will be switched ON two minutes after the ignition is switched OFF and the under hood temperature is above 194°F (90°C) and the fuel pressure is above 17 psi (1.2 bar). The pumps can operate for a maximum of eight minutes.

The after-run system uses two switches to turn the fuel pump ON and OFF. The coolant fan after-run switch, located next to the fuel pressure regulator, measures the under hood temperature and a pressure switch measures fuel pressure. The fuel pressure switch is located on the left side of the intake manifold in front of the throttle body. A fuel line from the fuel rail is attached to the switch.

The fuel pump after-run control unit, located in position 16 of the fuse/relay panel, also receives a signal from the fuel gauge sending unit. This signal is used to shut-OFF the fuel pump after-run system if the fuel level is below 1.5 gal. (5 liters).

FUEL SYSTEM COMPONENTS
These components are related to fuel and air delivery portion of the Digifant Fuel Injection system and will be addressed in this section.

^ Accelerator Pedal
^ Air Cleaner
^ Ambient Temperature Switch
^ Boost Control Valve
^ CO Adjustment Screw
^ CO Tap
^ Fuel Filter
^ Fuel Injector Insert
^ Fuel Injectors
^ Fuel Pressure Regulator (Diaphragm)
^ Fuel Pressure Switch
^ Fuel Pump
^ Fuel Pump Relay
^ Fuel Return Lines
^ Fuel Supply Lines
^ Fuel Tank
^ G-Charger
^ Idle Air Bypass Screw
^ Idle Mixture and Speed
^ Idle Stabilizer Valve
^ Intake Air Hoses
^ Intercooler
^ Throttle Cable
^ Throttle Valve