BOSCH Continuous Injection System (Cis): Operation: Notes

Depending on position of throttle valve, engine draws in more or less air. Ahead of throttle valve is an air funnel and an air flow sensor plate. This air flow plate is mounted on a pivoting lever and is counterbalanced. As more air flows into engine, sensor plate moves upward, thus opening wider a small metering slit, one for each cylinder. The size of the slit opening determines the amount of fuel injected under a constant pressure. In order to maintain a fuel pressure of precisely 4.5 bar (1 bar equals approximately 14.5 psi or 1 kg/sq. cm), a pressure relief valve is located in primary fuel circuit of fuel distributor. Excess fuel is diverted back to fuel tank. To assure that the quantity of fuel flowing through metering slits depends only on open area of slit, a pressure regulating valve (one for each cylinder) is used. In order to further control fuel quantity, counter pressure is used on top of fuel distributor plunger. The higher this pressure, the less the metering slits will be allowed to open and less fuel will be injected. Various control units control this counter pressure and are described below.