Diesel Engine Troubleshooting

Intake Air Temperature Sensor and Atmospheric Pressure Sensor

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This sensor is a semiconductor type sensor. It measures pressure utilizing the piezoelectric effect that when the pressure on the silicon element in the sensor changes, its electrical resistance changes. In addition, the air pressure on this sensor is switched between the pressure within the intake manifold and the atmospheric pressure, so both the intake air pressure and the atmospheric pressure are detected with one sensor. The switching between intake air pressure and atmospheric pressure is handled by the VSV (vacuum switching valve). When any one of the conditions below is established, the VSV is switched ON for 150 msec. by command of the engine ECU to detect the atmospheric pressure. When none of the conditions below is established, the VSV is switched OFF to detect the intake air pressure.

Atmospheric Pressure Measurement Conditions
– Engine speed = 0 rpm
– Starter ON
– Stable idling state

pic1 93 Intake Air Temperature Sensor and Atmospheric Pressure Sensor

Written by Jack

March 10th, 2019 at 11:54 pm

Fuel Temperature Sensor

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This is a thermistor type sensor that detects the fuel temperature. In the HP2, HP3, and HP4 systems, this sensor is installed on the supply pump unit, but in the HP0 system, it is installed on a leak pipe from an injector.

pic1 92 Fuel Temperature Sensor

Written by Jack

March 10th, 2019 at 11:52 pm

Coolant Temperature Sensor

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The coolant temperature sensor is installed on the cylinder block and detects the coolant temperature. This sensor is a thermistor type.

pic1 91 Coolant Temperature Sensor

Written by Jack

March 10th, 2019 at 11:51 pm

Mass Airflow Meter (with Built-In Intake Air Temperature Sensor)

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The mass air flow meter is installed behind the air cleaner and detects the intake air flow (mass flow). This sensor is a hot-wire type. Since the electrical resistance of the hot wire varies with the temperature, this characteristic is utilized to measure the intake air quantity. The mass airflow meter also has a built-in intake air temperature sensor (thermistor type) and detects the intake air temperature (atmospheric temperature).

pic1 90 Mass Airflow Meter (with Built In Intake Air Temperature Sensor)

Written by Jack

March 10th, 2019 at 11:50 pm

Intake Air Temperature Sensor

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The intake air temperature sensor detects the temperature of the intake air after it has passed the turbocharger. The sensor portion that detects the temperature contains a thermistor. The thermistor, which has an electrical resistance that changes with temperature, is used to detect the intake air temperature.

pic1 89 Intake Air Temperature Sensor

Written by Jack

March 10th, 2019 at 3:30 am

Accelerator Position Sensor

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• The accelerator position sensor converts the accelerator opening into an electric signal and outputs it to the engine ECU. There are two types of accelerator position sensor: the hall element type and the contact type. In addition, to provide backup in the event of breakdown, there are two systems and the output voltage is offset.

Hall Element Type
– This sensor uses a hall element to generate voltage from change in the direction of the magnetic field. A magnet
is installed on the shaft that rotates linked with the accelerator pedal, and the rotation of this shaft changes the magnetic field of the Hall element. The voltage generated by this change in the magnetic field is amplified by an amplifier and input to the engine ECU.

pic1 87 Accelerator Position Sensor

Contact Type
– The sensor uses a contact-type variable resistor. Since the lever moves linked with the accelerator pedal, the sensor resistance value varies with the accelerator pedal opening. Therefore, the voltage passing the sensor changes, and this voltage is input to the engine ECU as the accelerator opening signal.

pic1 88 Accelerator Position Sensor

Written by Jack

March 10th, 2019 at 2:01 am

Crankshaft Position Sensor (Engine Speed Sensor) and Cylinder Recognition Sensor {TDC (G) Sensor}

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Crankshaft Position Sensor (Engine Speed Sensor)
• The crankshaft position sensor is installed near the crankshaft timing gear or the flywheel. The sensor unit is a MPU (magnetic pickup) type. When the engine speed pulsar gear installed on the crankshaft passes the sensor section, the magnetic field of the coil within the sensor changes, generating AC voltage. This AC voltage is detected by the engine ECU as the detection signal. The number of pulses for the engine speed pulsar depends on the specifications of the vehicle the sensor is mounted in.

Cylinder Recognition Sensor {TDC (G) Sensor}
• The cylinder recognition sensor is installed on the supply pump unit for the HP0 system, but for the HP2, HP3, or HP4 system, it is installed near the supply pump timing gear. Sensor unit construction consists of the MPU type, which is the same as for the crankshaft position sensor, and the MRE (magnetic resistance element) type. For the MRE type, when the pulsar passes the sensor, the magnetic resistance changes and the voltage passing through the sensor changes. This change in voltage is amplified by the internal IC circuit and output to the engine ECU. The number of pulses for the TDC pulsar depends on the specifications of the vehicle the sensor is mounted in.

pic1 86 Crankshaft Position Sensor (Engine Speed Sensor) and Cylinder Recognition Sensor {TDC (G) Sensor}

Written by Jack

March 10th, 2019 at 1:07 am

EDU (Electronic Driving Unit)

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(1) General Description
• An EDU is provided to enable high-speed actuation of the injectors. The EDU has a high-voltage generation device
(DC/DC converter) and supplies high voltage to the injectors to actuate the injectors at high speed.

pic1 84 EDU (Electronic Driving Unit)

(2) Operation
• The high-voltage generating device in the EDU converts the battery voltage into high voltage. The ECU sends signals to terminals B through E of the EDU in accordance with the signals from the sensors. Upon receiving these signals, the EDU outputs signals to the injectors from terminals H through K. At this time, terminal F outputs the IJf injection verification signal to the ECU.

pic1 85 EDU (Electronic Driving Unit)

Written by Jack

March 10th, 2019 at 1:06 am

Engine ECU (Electronic Control Unit)

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The engine ECU constantly ascertains the status of the engine through signals from the sensors, calculates fuel injection quantities etc. appropriate to the conditions, actuates the actuators, and controls to keep the engine in an optimal state. The injectors are actuated by either the EDU or the charge circuit in the engine ECU. This actuation circuit depends on the specifications of the model it is mounted in. The ECU also has a diagnosis function for recording system troubles.

pic1 83 Engine ECU (Electronic Control Unit)

Written by Jack

March 10th, 2019 at 1:02 am

Engine Control System Diagram

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pic1 82 Engine Control System Diagram

Written by Jack

March 10th, 2019 at 1:00 am

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