Download The electro-hydraulic actuator is bolted to the side of the fuel distributor. It consists of a plate valve fastened between two electromagnets. By varying the electric current to the electro-hydraulic actuator and changing the strength of the magnets, the plate valve can be moved. The varying position of the plate valve controls the quantity of fuel allowed into the lower chamber of the fuel distributor, causing the differential pressure to vary. The operating range is from -50 to +150mA. Differential pressure will be from 0 bar to about 1.6 bar (24 PSI) less than system pressure. The electro-hydraulic actuator is constructed so that without any operating current, such as in an electrical failure, the plate valve would deflect enough under system pressure to maintain a differential pressure of about 0.4 bar. This combined with the 0.2 bar difference caused by the pressure regulating springs in the fuel distributor will result in a difference of 0.2 bar between the upper and lower chambers in the fuel distributor. Since this pressure difference is the same as on the earlier CIS system, the car will still be driveable in the event of an electrical failure. However, it will run roughly because of the resultant lean air/fuel mixture.
Home Tips & Tricks 1989 Mercedes Benz 420SEL Differential Pressure Regulator Description and Operation