Fuel Delivery and Air Induction: Description and Operation

Fuel Control:

SYSTEM DESIGN
Bosch Motronic 1.8 fuel injection is a multi-point, pulsed electronic fuel injection system. It is designed to deliver a precise amount of fuel to each cylinder under various engine speed and load conditions.

BASIC OPERATION
Fuel is delivered under pressure to the fuel rail by two fuel pumps; an in-tank pump and a main pump. Fuel pressure in the fuel rail is held constant by a fuel pressure regulator. The fuel rail supplies fuel to six electric solenoid type fuel injectors. Since fuel pressure is held constant, the amount of fuel that is injected is determined by the length of time the injectors are open (injection duration).

Fuel injection duration is controlled by the ECU. The ECU determines injection duration by measuring various engine input signals and evaluating the signals in relation to pre-programmed values. Injection occurs every other engine revolution for each pair of injectors (parallel injection).

Several notable features of Motronic 1.8 fuel systems include:
^ Adaptive memory,
^ Self-diagnostics with fault code storage,
^ "Limp home" operating mode,
^ Anti-knock enrichment.


ADAPTIVE MEMORY
Time and mileage affect the operation of both the injection and the idle control systems. To compensate for wear and deposit accumulation, the system modifies its basic programming (within a "window" of operation) to provide efficient operation under all driving conditions.
If the system determines that it must modify its basic programming beyond the "window", a fault code is stored in the self-diagnostic memory.

SELF-DIAGNOSTICS
The self-diagnostic system is a built-in function of the ECU. The ECU constantly monitors engine performance by comparing its programming "window" with the values it receives from various sensors. When a programming parameter has been exceeded, a retrievable fault code is stored. If a serious fault is detected, the ECU illuminates a "CHECK ENGINE" light on the instrument panel.

LIMP HOME OPERATION
If the ECU determines that the air mass meter signal is incorrect, the system enters a pre-set "limp home" function. In "limp home" mode, a pre-set injection duration allows the vehicle to be driven to the nearest garage.

ANTI-KNOCK ENRICHMENT
If ignition knock cannot be counteracted by retarding ignition timing, the ECU provides a richer mixture to reduce combustion temperature.


FUEL SYSTEM COMPONENTS
The components addressed for the fuel system are:
^ Accelerator pedal
^ Air filter
^ Fuel filter
^ Fuel injectors
^ Fuel pressure regulator
^ Fuel pump
^ Fuel rail
^ Fuel return line
^ Fuel supply line
^ Fuel tank
^ In-tank fuel pump
^ Intake air hoses
^ Throttle body
^ Throttle cable

For additional FUEL SYSTEM related components,