Ckp Sensor; Scv; Ft Sensor; Common Rail Pressure Sensor - Isuzu 4HL1 Workshop Manual

1A-12 Engine Control System

CKP Sensor

The CKP (crank position) sensor is installed to the
flywheel housing and, when flywheel teeth pass the
sensor, a CKP signal is generated. The ECM identifies
the cylinder from the CKP signal as well as the CMP
signal sent from the CMP sensor and determines the
crank angle, and uses this angle in fuel injection control
and engine speed calculation. These tasks are usually
performed based on the CKP signal but if the CKP
sensor fails, the CMP signal will substitute for the CKP
signal.

FT Sensor

The FT (fuel temperature) sensor is installed to the
supply pump and the thermistor in the sensor alters the
resistance in response to the temperature change. The
resistance is decreased when the fuel temperature is
high while increased when the temperature is low. The
ECM supplies 5 V to the FT sensor via pull-up
resistance and calculates the fuel temperature from the
change in voltage and uses it in supply pump control
and other control tasks. This voltage is decreased
when the resistance is small (the temperature is high)
while increased when the resistance is large (the
temperature is low).

SCV

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The SCV (suction control valve) is installed to the
supply pump and controls the suction fuel quantity. The
SCV is fully opened in normal state and larger drive
voltage (duty) results in smaller opening. The ECM,
based on the data acquired from sensors, calculates
the desired common rail pressure and pump flow rate
and compares the calculated desired common rail
pressure to the actual value to determine the SCV
opening. When the actual pressure is lower than the
desired value, the SCV is opened to increase the pump
flow rate. When the actual pressure is higher than the
desired value, the SCV is closed to decrease the flow
rate.

Common Rail Pressure Sensor

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The common rail pressure sensor is installed to the
supply pump, and detects the fuel pressure in the
common rail, converts the pressure into a voltage
signal, and sends the signal to the ECM. Higher
common rail pressure provides higher voltage while
lower pressure provides lower voltage. The ECM
calculates actual common rail pressure (fuel pressure)
from the voltage signal and uses the result in fuel
injection control and other control tasks.
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