Work in different modes (VW Passat B4)

Operation under load conditions

The fuel electric pump takes fuel from the fuel tank and pumps it under a pressure of about 5 kgf/cm² into the dispenser-distributor through the fuel filter and pressure accumulator.

Fuel under supply pressure fills the lower chambers of the metering distributor and presses the diaphragms of the differential pressure valves to the fuel supply pipes to the injectors. Fuel under pressure penetrates into the upper chambers of the metering distributor through the slots in the walls of the distribution plunger. The amount of fuel entering the upper chambers of the metering distributor changes depending on the vertical movement of the distribution plunger. When the total fuel pressure in the upper chambers and the spring pressure exceed the fuel supply pressure in the lower chambers, the valve diaphragms drop, opening access of fuel through the pipe to the injection nozzle. As soon as the pressure in the upper chambers of the metering distributor decreases, the valve diaphragms return to their original position. Due to the uniform periodicity of opening and closing of the fuel supply channels to the injectors, a constant fuel pressure is established. The displacement of the air flow meter pressure disc is transmitted via the lever to the distribution plunger, the return of which to its original position occurs due to the counteracting fuel pressure in the upper part of the metering distributor.



The counter pressure is created by the supply pressure and is regulated by the control pressure regulator. The bypass valve installed in the throttle valve area ensures a minimum vacuum in the air flow meter when the engine is idling. The degree of valve opening is regulated by a needle.

Cold engine starting and idling

The fuel electric pump creates the working pressure of the fuel in the system. At the moment of starting a cold engine and for a certain time, the starting injector injects an additional amount of fuel into the intake manifold. The duration of the starting injector operation is determined by the thermal time regulator depending on the temperature of the coolant.

The electromagnetic valve of stabilization of idle speed is installed in the air channel, made parallel to the throttle valve. The valve provides the supply to the engine of additional quantity of air to increase the speed of the crankshaft of a cold engine at idle speed and to maintain the number of revolutions of idle speed within the specified limits (950-1050 rpm). The degree of valve opening is set by the electronic unit of idle stabilization and forced idle control depending on the temperature of the coolant and the engine crankshaft speed. Additional enrichment of the fuel-air mixture during starting and warming up of a cold engine is achieved due to a greater lift of the distributor plunger due to the fact that the control pressure regulator reduces the counteracting pressure.

Until the engine is warmed up, the bimetallic spring compresses the diaphragm valve spring, opening the fuel drain channel, which leads to a decrease in the control pressure on the distribution plunger.

Starting a hot engine

To completely eliminate fuel evaporation after the engine has stopped, the pressure in the injection system is maintained for some time by a pressure accumulator, which temporarily interrupts the flow of fuel into the tank.