Function of ECU - Fuel Injection

:

In the control unit, the airflow meter voltage which is proportional to the air quantity per time unit is divided by engine speed in digital processing. This corresponds to the air quantity taken in per stroke and represents the uncorrected basic injection time.

In order to compensate the valve operating and releasing time depending on battery voltage, the ignition time is extended by the battery voltage correction time. The injection valves are actuated according to the corrected basic injection time.

An adjustable map which is controlled by the oxygen sensor is superposed on this basic anticipatory control signal. Now by interpolation of the basic injection time, a fuel/air mixture which is optimized for low exhaust gas emission and fuel consumption at every engine speed-load point can be obtained.

With the throttle valve closed during idling or coasting, the lowest oxygen value line is chosen. This enables a precise enrichment in coasting operating at low engine speed in order to achieve good combustion.

At full load a speed-dependent full load operation becomes effective which allows the minimum enrichment required for maximum performance.

Due to the small, strongly pulsating air quantity available during starting, a fixed value of the air quantity signal is set to determine the injection time. A correction depending on cooling water temperature increases the injection time at cold engine in order to supply the additional quantity of fuel required. At a very low starting temperature, the aforementioned cold start valve starts to operate additionally. In order to achieve a combustion improvement on cold engine directly after the start, a warm-up enrichment depending on coolant temperature and time is provided.

Additionally, an enrichment which depends on coolant temperature is operating for adaption of the mixture during the warm-up phase. In order to compensate variations of air density at different air temperature, the intake air temperature measured in the airflow sensor is used as correction factor for the injection time. An acceleration enrichment depending on engine temperature is made in order to improve the gas intake and to reduce NO peaks during acceleration phases. A deceleration cutoff serves to provide fuel economy during coasting. Due to the idle speed rise at cold engine, the injection is interrupted above 1800 rpm and at warm engine above 1360 rpm.

It starts to operate again at 400 rpm below the above given figures.

To achieve engine speed limitation, the fuel injection is switched off at the maximum permissible engine speed of 5000 rpm - 2.7 liter; (6600 rpm - 3.2 liter).

The control of the fuel pump represents a further function of the control unit. It is switched on over a relay when the starter is actuated; Terminal 50. An engine speed control assures that the fuel pump operates only with the engine running.