EHA, elctro hydraulic actuator. So the controller is going to administer varying current flow through this device. The current flow is going to deflect valving thru magnetism to allow a very precise internal fuel leak.
Internal pressure on both sides of the diaphram separating the two halves of the distributer hold the delivery valves shut and no fuel flows. The lower chamber is fed through an oriface that allows the bottom chamber to be reregulated to a lower pressure. Under normal, zero current, flow the pressure differential (upper to lower) is .4bar. A 60ma negative current shuts off flow causing there to be no differential pressure and no fuel flow - decel cut-off. Cold, starting, enrichment is about +60ma or more. This runs the differential pressure to over a bar. Normal driving control runs in the -10 to =10ma range and this is about .1bar in the differential pressure.
Usually the fuel pressures follow the electrical control and just monitoring the electrical is all that is needed. But if what is happening electrically doesn't follow the symptoms it can be necessary to veryfy that what the electrical is supposed to do actually happens.
Bosch Master, ASE Master, L1
33 years MB technician