Fuel Injection Pump
The Bosch single plunger mechanical pump consists of a low-pressure, vane-type fuel pump, a high-pressure distributor-type plunger injection pump, a centrifugal governor, and an injection timing advance mechanism. Pumps are equipped with an electrical fuel shut-off solenoid. See Fig 1 .
As the vane type pump rotor turns, centrifugal force holds the vanes against the walls of the pump's pressure chamber. The offset design of the rotor and pressure chamber, squeezes trapped fuel between vanes and forces it out the delivery port. Turbo models have a boost compensator to enrichen the fuel mixture under turbo boost conditions. See Fig 2 .
Vane pressure of the pump is 65-73 psi (4.6-5.1 kg/cm2 ) at 1600 RPM or 87-94 psi (6.1-6.6 kg/cm2 ) at 2200 RPM. The main pump increases this pressure to approximately 1800 psi (126 kg/cm2 ).
The amount of fuel injected is controlled by changing the injection cut-off point according to engine speed and load conditions. The cut-off point is controlled by the position of the metering sleeve around the distributor plunger. The sleeve normally covers a relief port in the plunger. Uncovering the port stops injection.
The sleeve position is determined by a centrifugal governor, and accelerator linkage. A large quantity of fuel is supplied during starting, and less at idle. No fuel is allowed to pass when the engine exceeds a predetermined maximum RPM.