1 - | Description of the system

General information on the fuel injection-ignition system
The integrated electronic control system, with ignition and injection both controlled by the same control unit, ensures optimal engine performance and output, thus reducing fuel consumption and harmful exhaust emissions. This system ensures an accurately metered air-fuel ratio and optimal management of ignition advance.
The system consists of three different circuits:
Fuel circuit
Air intake circuit
Electrical circuit (with control unit, sensors and actuators).
Importance of the air-fuel mixture and the ignition advance.
Correct management of the air-fuel ratio and the ignition advance are fundamental requirements for optimal engine operation.
The air-fuel mixture is given by the ratio, in weight, of air to fuel taken in by the engine: the ideal or stoichiometric ratio is that which determines complete combustion. Excessive or insufficient air give rise to, respectively, a lean (or weak) mixture or a rich mixture, which affect power and consumption, as well as emissions of exhaust gases.
Electronic control of ignition timing advance makes it possible to optimise the performance of the engine, maximum power output, fuel consumption and the concentration of exhaust pollutants.
Electronic ignition timing control combined with fuel supply control allows for optimal engine operation in all conditions of use (low temperature start, warm-up stage, transitory acceleration/deceleration stages, engine under partial load, full load, idle).
Siemens M3C fuel injection-ignition system
The Marelli injection-ignition system is the Alfa/N type, in which the engine speed and throttle position are used as the main parameters for measuring the quantity of intake air. If the quantity of air is known, the quantity of fuel can be dosed accordingly to obtain the required ratio. Additional sensors in the system (engine rpm, aspirated air pressure, air temperature, engine oil temperature and lambda sensor to control CO level) are used to adjust the basic engine control strategy in accordance with the operating conditions. The engine speed and the throttle angle are also used to calculate the optimal ignition advance for all operating conditions. The quantity of air taken in by each cylinder during each cycle depends on the density of the air in the intake manifold, the cylinder capacity and the volumetric efficiency.
The volumetric efficiency of the engine is determined experimentally throughout the entire range of operating conditions (rotation speed and engine load conditions). The values obtained in this way are then used for the generation of a map which is stored in the Flash EPROM of the Siemens M3C ECU for injection control. The Flash Eprom can be programmed via CAN line. Fuel injection control is of the phased sequential type, i.e. the injectors are not operated in parallel. Fuel delivery to each cylinder may start during the expansion stroke and may extend up to after the beginning of the induction stroke. Fuel cut-off timing (the time when the injectors are closed), is saved onto a special map, which is stored in the ECU Flash Eprom. Ignition is of the static inductive discharge type, featuring dwell time control so as to ensure coil charging at steady power Power modules for coil power supply are included in the ECU hardware. Advance curves are stored in the ECU Flash Eprom. Both coils and power modules are controlled by the ECU, which calculates the ignition advance.
Notes
To test the components and wiring of the injection - ignition system, use the “DDS” tester, following the indications given in the paragraph “Guided diagnosis” (Sect. D 5).
Key to the sensor position diagram

1 | Injection ECU

2 | Injection relay

3 | Fuel pump

4 | Lambda sensor (horizontal cylinder)

5 | Engine temperature sensor

6 | Air temperature sensor

7 | Horizontal cylinder coil

8 | Pressure sensor

9 | Engine speed sensor

10 | Vertical cylinder coil

11 | Sparkplug

12 | Throttle position sensor

13 | Injectors

14 | Lambda sensor (vertical cylinder)

Fuel circuit
Fuel from the tank is pumped into the fuel feed line (OUT) and then to the injectors, by means of a pump located on a flange installed at the bottom of the fuel tank. The flange also incorporates the pressure regulator that controls the fuel feed pressure and keeps it constant at a higher value than the negative pressure generated by the engine. Fuel that is not injected in the intake hoses returns to the flange and then to the tank by way of a return hose (IN).
Air circuit
The air circuit is composed of two intake manifolds (A), the throttle body (B) and an airbox (C) located over the throttle body.
The engine control system (ignition and injection) relies on several sensors which adjust the mixture according to the air pressure and temperature and the engine load. An air temperature sensor (6) located on the intake manifold of the vertical cylinder and an air pressure sensor (5) located between the “V” of the engine block, connected to the air intakes, measures the atmospheric pressure and transmits this information to the ECU where it used to make essential adjustments to the quantity of fuel injected when the motorcycle is ridden at varying altitudes (e.g. a route that starts at sea level and ends at a high altitude); they also allow the ECU to make mixture corrections in relation to air density. Assuming that the volume of air is constant, if the temperature rises, oxygen content will decrease, whereas it will increase as the temperature falls.
If the temperature rises, the mixture should be leaner, while if it falls, the mixture should be made richer to maintain the best air‑fuel ratio.
The two lambda sensors (4) and (14), installed respectively in the horizontal and vertical cylinder exhaust pipes, provide information that is used by the ECU tocontrol the air-fuel mixture.
There is a throttle position sensor (12) fitted on the spindle of the rear cylinder throttle. This device sends the ECU a signal that is an indirect indication of the quantity of air aspirated by the engine (indirect measurement of engine load).
Operating phases
Normal operation
When the engine is warm, the unit calculates injection time and the ignition advance using the values stored in the respective maps, in accordance with the RPM and throttle position. The calculated quantity of fuel is fed to each cylinder through the injectors in one single sequential delivery.
Starting
When the ignition switch is turned to ON, the control unit activates the fuel pump for a few moments to pressurise the fuel supply circuit. The throttle position and engine temperature signals are processed. When the engine is turned over by the starter motor, the unit receives the engine RPM and timing signals that allow it to proceed with injection and ignition. To facilitate start-up, the mixture is enriched in accordance with engine temperature During starting, the ignition advance angle is maintained at 0° until the engine starts. When the engine starts, the ECU controls the ignition advance in accordance with the values stored in the map and makes any necessary corrections according to the air and engine temperatures.
Acceleration/deceleration
During acceleration, the ECU makes the mixture richer for improved engine performance. Acceleration is detected by monitoring the speed at which the rider turns the twistgrip to open the throttle. During a rapid deceleration, determined by the rider quickly turning the twistgrip to close the throttle, the ECU makes the mixture leaner to reduce emissions and fuel consumption.