The control unit can also control other output functions, such as engine speed limiting. When actual engine speed reaches a programmed maximum, the fuel injection pulses can be suppressed. In some systems the fuel injectors are turned off at a pre-set engine speed. Once the engine speed has slowed to a safe value the injectors are turned back on. This is referred to as a hard limiter. Other systems use soft limiters where once a pre-set engine speed has been reached, the injector pulse width is reduced to prevent the engine from turning any faster.
Both systems protect the engine from over-revving, without disadvantaging its operation.
The ECU can control the fuel pump. For safety reasons, when the ignition is turned on and the engine is stationary, the fuel pump operates for a few seconds only, enough to prime the engine for starting. It starts again during cranking, and when the engine is running above a specified minimum number of revolutions per minute.
Some exhaust gas is allowed to re-circulate, to control the nitrogen oxides. How much exhaust gas does this, can be controlled, by vacuum and vent solenoids, in the vacuum circuit of the EGR valve.
When loads are put on the engine, such as from air-conditioning or lights, the control unit regulates how much the idle speed control valve opens, to maintain a pre-set idling speed.
Fuel vapors stored on the active material in the canister are drawn into the cylinders and burned when engine operating conditions allow.
At different engine speeds and loads, the control unit operates solenoid valves that alter the effective pipe length of the manifold. This extends the torque output over a wider range of engine speeds. The cooling fan is switched on automatically when the air-conditioning is switched on. Instantaneous fuel consumption can be displayed on the instrument panel in front of the driver.
