Single Point Injection

In the meantime, the single point injection is clearly on it's way out. Whereas it was previously found in engines with up to two liters of capacity, nowadays, it is installed, at most, in engines of half that size. The reason lies mainly in the exhaust gas regulations which are becomming more and more stringent, an engine without differentiation between the individual cylinders can no longer keep up. Modern multi-point injection systems deliver far better results, are however, noticeably more complicated.

The first electronically controlled central injection was developed in 1974 by GM. Later Bosch involved themselves with the Mono-Jetronic. There is only one injector-valve for all the cylinders, which injects intermittently above the throttle flap. The injection amount is regulated by the opening timing.
In the beginning, because of the lower supply pressure of 0,75 to 1 bar, only a single-stage turbine pump is installed. The system pressure regulator has, as opposed to the Multi-point injection , no vacuum connection, because the system pressure regulation is independent of the vacuum pressure. The injection amount is exclusively dependent on the injection time, because the injection takes place above the throttle flap and not in the vacuum area. The system pressure regulator can be seen below the injector-opening in figure 3.
Apart from the Lambda sensor, the throttle flap potentiometer (figure 4 on the far right) is an important sensor for the determining of the injection amount. In addition, the control device still also needs the air- or the coolant temperature and the relationship to the crankshaft.The Mono-Jetronic (Bosch) controls the idling through a servo-motor with worm-drive, the Multec (GM) does it through a bypass.

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