Description & Operation
The Bosch Continuous Injection System (CIS) is a mechanical system. Its entire operation is based upon the metering or sensing of the amount of intake air required to run the engine under different conditions. All intake air must pass through the mixture control unit which contains an air sensor plate within a cone shaped venturi.
Sensor plate is movable and is very sensitive to the incoming flow of air. Plate is mounted on a pivoting lever which is connected to a fuel control piston (plunger) in the fuel distributor. As the sensor plate is raised or lowered by differences in amount of air flow, the plunger is raised or lowered in the fuel distributor and determines amount of fuel to be injected into each cylinder.
System is made up of airflow sensor, fuel distributor), control pressure regulator, auxiliary air valve, auxiliary air regulator, thermo-time switch/valve, cold start valve, injectors, electric fuel pump(s), fuel accumulator, a fuel filtering system, and connecting lines and hoses.
On 1978-79 911SC, 928, and 930 Turbo models, the control pressure regulator vacuum connections have been reversed. The tapping below the throttle is now connected to the side of the regulator rather than the top. Control pressure regulators on 911SC and 930 Turbo work differently.
On 1978-79 911SC, when engine is stationary or vacuum is low, control pressure is low. Only the external spring is effective on control valve. At idling, internal spring is activated as diaphragm is lifted by vacuum. Control pressure is increased. Near full throttle, vacuum decreases, the internal spring pressure decreases and control pressure is lowered. Fuel mixture becomes richer. On 1978-79 930 Turbo, when engine is stationary, during normal operation or at low boost pressures up to about 1.5 psi (.1 kg/cm2 ), both springs are effective and control pressure is high. A drop in pressure (full throttle enrichment) takes place when a pressure in excess of 1.5 psi (.1 kg/cm2 ) exists above the diaphragm. Full throttle enrichment cannot be checked until boost pressure reaches about 4.35 psi (.3 kg/cm2 ).