Fuel Delivery and Air Induction: Description and Operation

Digifant I Engine Management System:

MOTRONIC FUEL INJECTION SYSTEM
The Motronic Engine Management System combines the engine's ignition and fuel injection functions into one system, managed by a single electronic control unit (Motronic Control Unit). With the Motronic system, basic fuel metering is determined by engine rpm and by the volume and temperature of the air entering the engine. The Motronic Control Unit receives air flow volume and temperature data from the Air Flow Sensor as well as engine rpm data from the ignition system, and distributes fuel 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 Motronic 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. Two separate electric Fuel Pumps feed filtered fuel to the Fuel Rail, the Fuel Transfer Pump that is mounted inside the Fuel Tank and the main Fuel Pump located under the car.

The Motronic 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 Motronic Control Unit with information on engine combustion efficiency by measuring the amount of oxygen in the exhaust stream. A throttle valve potentiometer on the throttle valve informs the Motronic Control Unit when the throttle is fully open or fully closed (at idle). A coolant temperature sensor provides the Motronic Control Unit with engine coolant temperature information for adjustments it will make during starting and warm-up.

In order for the Motronic Fuel Injection System to operate properly, the basic adjustments to idle speed, ignition timing, idle air/fuel mixture and throttle valve potentiometer must be correct. If these basic settings are faulty or slightly misadjusted, the Motronic 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 SYSTEM COMPONENTS
These components are related to fuel and air delivery portion of the Motronic Fuel Injection system and will be addressed in this section.

^ Accelerator Pedal
^ Air Cleaner
^ CO Adjustment Screw
^ CO Tap
^ Fuel Filter
^ Fuel Injector Insert
^ Fuel Injectors
^ Fuel Pressure Regulator (Diaphragm)
^ Fuel Pump
^ Fuel Pump Relay
^ Fuel Reservoir
^ Fuel Return Lines
^ Fuel Supply Lines
^ Fuel Tank
^ Fuel Transfer Pump
^ Idle Air Bypass Screw
^ Idle Mixture
^ Idle Speed
^ Intake Air Hoses
^ Idle Stabilizer Valve
^ Intake Manifold
^ Throttle Cable
^ Throttle Valve