Isuzu 4JA1 Workshop Manual page 531

The timing control valve (TCV) acts as a variable
throttle, using the rapid opening and closing (cycling)
of the valve needle in the TCV. At normal operation,
the TCV controls the pressure acting on the annular
chamber so that the hydraulic stopper cam move to
any position, from the retard position to the advance
position. At this time, the duty ratio is set by the fuel
injection pump control unit (PCU).
When control current flows to the TCV coil, the valve
needle opens and the fuel annular chamber flows
through the orifice to the feed pump inlet.
Consequently, the pressure of the annular chamber
decreases and the hydraulic stopper is moved to the
retard side.
When control current to the TCV coil is cut, the valve
needle closes and the return passage is closed.
Consequently, the pressure of the annular chamber
increases and the hydraulic stopper is moved to the
advance side.
Pump Camshaft Position (CMP) Sensor
Legend
1. Pump Camshaft Position (CMP) Sensor
2. Flexible Connecting Harness
3. Drive Shaft
4. Pump Camshaft Position (CMP) Sensor Retaining
Ring
5. Sensor Wheel
When the drive shaft rotates, the pump camshaft
position (CMP) sensor receives signal form the sensor
wheel, and an electric pulse is sent through the flexible
connecting harness to the fuel injection pump control
unit (PCU). From these signals the PCU can determine
the average pump speed and the momentary pump
speed. The pump CMP sensor is mounted to the cam
ring. Thus, the relationship between the cam ring and
the pump CMP sensor signal is constant. The pump
CMP sensor signal is utilized for the following purposes:
• To determine the momentary angular position of
the cam ring.
• To calculate the actual speed of the fuel injection
pump.
• To determine the actual timing plunger position.
Legend
1. Pump Camshaft Position (CMP) Sensor Signal
2. Crankshaft Position (CKP) Sensor Signal
3. Fuel Injection Solenoid Valve Control Pulse
4. Fuel Injection Solenoid Needle Valve Lift
RTW66ESH003301
5. Cam Lift (Cam Profile)
6. Pulse Count
7. Fuel Injection Solenoid Valve Close
8. Fuel Injection Solenoid Valve Open
9. Start of Pressure Delivery
10. End of Pressure Delivery
11. Pressure Delivery Angle
12. Effective Stroke
Engine Control System (4JH1) 6E-277
RTW66ESH003401