User Manual

• ECM
• Sensor for the Injection Actuation Pressure (IAP)
• Pump control valve
The closed loop circuit works in the following manner:
• The ECM determines a desired actuation pressure by gathering information from sensor inputs and
software maps.
• The ECM monitors actual actuation pressure through a constant signal voltage from the IAP sensor.
• The ECM constantly changes control current to the pump control valve. This changes the pump outlet
flow.
There are two types of actuation pressure:
• Desired actuation pressure
• Actual actuation pressure
Desired actuation pressure is the injection actuation pressure that is required by the system for optimum engine
performance. The desired actuation pressure is established by the performance maps in the ECM. The ECM
selects the desired actuation pressure. The selection is based on the signal inputs from many sensors. The ECM
is getting signal inputs from some of the following sensors: throttle position sensor, boost pressure sensor,
speed-timing sensors and coolant temperature sensor . The desired actuation pressure is constantly changing.
The change is based on various signal inputs. The changing engine speed and engine load also cause the desired
actuation pressure to change. The desired actuation pressure is only constant under steady state conditions
(steady engine speed and load).
Actual actuation pressure is the actual system pressure of the actuation oil that is powering the injectors. The
ECM and the pump pressure regulator are constantly changing the amount of pump outlet flow. This constant
changing makes the actual actuation pressure equal to the desired actuation pressure.
Pump Control Valve Operation
The pump control valve has the following three stages:
• Valve operation (engine off)
• Valve operation (cranking the engine)
• Valve operation (running engine)
Valve Operation (ENGINE OFF)
When the engine is off, there is no pump outlet pressure from the pump and there is no current to the control
valve solenoid from the ECM. The actuator spring pushes the actuator piston completely to the left. The idler
which is not shown and the sliding sleeves are moved to the left also. At this point, the pump is in the position
of maximum output.
Valve Operation (ENGINE CRANKING)
During engine start-up, approximately 6 MPa (870 psi) of injection actuation pressure is required in order to
activate the unit injector. This low injection actuation pressure generates a low fuel injection pressure of about
35 MPa (5000 psi). This low fuel injection pressure aids cold starting.